Right Side Up: Rye & Rhubarb Upside-Down Cake

May 20, 2016
Cakes, Fruit Desserts

Soooooo, I am hardcore fangirling over rye flour right now. (Yes, those are the sorts of things that bakers fangirl over.) For that matter, I’m fangirling over rhubarb, but I guess that happens every spring nowadays, doesn’t it? Normally, I am fairly lukewarm when it comes to fruit desserts; I will almost always choose chocolate or caramel over fruit. But this. THIS. I was blown away by the beauty, complexity, and uniqueness of Yossy Arefi’s Rye & Rhubarb Upside-Down Cake from her new Sweeter Off the Vine. While its jewel-toned fruit is striking, it is at the same time unassuming and unexpected. It is not a showy 3-layer cake slathered in luxurious frosting; instead, it is a simple, single-layer number that might get overlooked. But this would be a tragic mistake. What’s so special, you ask? The flavor combination and texture of this little cake will leave you thinking about it long after you’ve devoured the last crumb. The tanginess imparted by the rye flour, especially combined with buttermilk, is the perfect juxtaposition for that sweet-tart rhubarb. (And may I just pause and say that the word “tanginess” makes me cringe in relation to this cake for some reason, but that really is the closest word that seems accurate.) This is one of those what-is-in-there?! cakes; there’s definitely vanilla, but there is also a certain magical flavor that is hard to put one’s finger on, and that is what makes rye flour so special. I only recently discovered it when I made these Whiskey & Rye Chocolate Chip Cookies over the holidays, and now I squeal like a little girl when I come across new rye recipes. In a word, I am enamored with both of these starring ingredients, and together they are positively dreamy. The only thing that makes this cake even better? A dollop of freshly whipped cream on top.

I have to say, I am not the most adept with rhubarb– it is still a relatively new ingredient for me to work with, and I’ve had to redo some of the things I’ve made with it. I was sweating this one because I had been looking high and low for rhubarb (where were all these Instragrammers finding it in early April?), and I finally found some beautiful stalks at Oxbow Public Market in Napa. I was not about to let those babies go to waste! Unfortunately, I assumed that I would need to remake this as soon as I flipped it onto its platter because it was not visually what I was hoping for; I was sure the whole thing would collapse, what with the pieces of rhubarb sliding off immediately. But despite the aesthetic imperfections, the cake itself was perfectly tender, yet sturdy– and so.very.delicious. The rhubarb juices soak into the cake, blurring the line between fruit and cake in the most lovely of ways. I was blown away, and I wanted to get it right, so I went ahead and remade the cake to correct my errors.

It’s not a difficult cake per se, but I did learn a few things by making it twice:

Where the recipe says not to let the rhubarb fall apart while cooking on the stove, it’s not just a friendly suggestion. The first time, I way overcooked it, such that pieces were completely falling apart. I ended up straining the rhubarb syrup right over the cake pan to keep out all the mushiest pieces. On the second attempt, I still overcooked them a bit– some pieces had started to fall apart when I turned my back for just a moment. It’s tricky because some stalks are firmer than others. Cut any wide or thick ones in half lengthwise so you have fairly uniform pieces, and watch them very carefully towards the end of cooking. Some of mine were too soft and therefore unusable, but most were okay. I only used about ¾ of the juices in the pan the second time. (I think this is a matter of preference.) Also, I used 1 pound of rhubarb after trimming, since the first time I didn’t have enough to cover the bottom of the pan, and I would say you could even use more. (I first saw the recipe at A Cozy Kitchen, who cooked the rhubarb perfectly, and it looks like maybe she didn’t use much of the syrup?)
I used a gorgeous, plump Tahitian vanilla bean that one of my besties hand-carried for me from Tahiti– so fragrant and syrupy! Use the best vanilla that you can here– I think even a good quality vanilla bean paste would work.
You can use either a 3″ deep cake pan or a springform pan, and I used the latter because I didn’t have a super deep regular pan (though one has since been acquired). In the future, I would not use the springform pan. I had to remove the ring before flipping the cake, which a) was a precarious two-person job, and b) allowed some of the over-cooked rhubarb pieces from that first attempt to slide off the top of the cake. It would be a hell of a lot easier to flip the cake out of a regular pan onto a platter. Furthermore, quite a lot of the rhubarb juice leaks from the bottom of pan almost immediately, so you lose a lot by the time the cake is baked.
To further avoid the problem of losing fruit pieces, the second time I let the cake cool in the pan for a good hour or so (much longer than the recommended 15 minutes), and it came out soooo much prettier and neater, with clean edges and all fruit intact. While it’s delicious warm, I felt that the cake was too hot and fragile to flip so soon.

I am absolutely elated with this cake– it’s an immediate favorite, and I wish I could make it all year round! Oh, and not incidentally, I usually bring my baked goods to share at work, but this cake I kept to hoard at home… both times. 😉

Rye & Rhubarb Upside-Down Cake
Adapted from Sweeter Off the Vine by Yossy Arefi
Yields 1 9″ cake

For the rhubarb topping:

1 pound (450g) trimmed rhubarb, cut into 2-inch lengths (cut wide pieces lengthwise for even cooking)
Seeds scraped from 1 vanilla bean (reserve pod for another use)
¾ cup (150g) granulated sugar
¼ cup (55g/4 tablespoons/½ stick) unsalted butter
1 teaspoon grated lemon zest
Pinch fine sea salt

For the rye cake:

1 cup (125g)  all-purpose flour
1 cup (130g) dark rye flour
1 tablespoon baking powder
½ teaspoon baking soda
½ fine sea salt or 1 teaspoon kosher salt
½ cup (115g/8 tablespoons/1 stick) unsalted butter, at room temperature
½ cup (100g) granulated sugar
2 large eggs, at room temperature
1 teaspoon pure vanilla extract or vanilla bean paste
1½ cups (355ml) buttermilk, at room temperature

For serving (optional, but highly recommended):

Lightly sweetened whipped cream or vanilla/strawberry ice cream

Preheat an oven to 375°F and position a rack in the center. You will need a 3” deep pan– either a 9” round cake pan or a springform pan; grease the pan and line the bottom with a circle of parchment paper, then grease the paper. Dust the paper and sides with flour, knocking out the excess. (The flouring step was not necessary with a springform pan, but I would definitely do it if using a standard pan.)

Place the sugar, butter, vanilla seeds, lemon zest, and salt in a skillet and gently stir together over medium-low heat. When the sugar and butter begin to melt together, add the rhubarb, stirring to coat the pieces with sugar. Cook the rhubarb for about 6-8 minutes, until it is tender, bubbling with juices, and a little caramelized (but still intact), stirring the contents of the pan occasionally. Important: Do not cook until the point where the rhubarb is falling apart—cutting the rhubarb into similarly-sized pieces helps them cook evenly. Pour the rhubarb and juices into the prepared cake pan and arrange the pieces in a single layer across the bottom. If you don’t have enough to completely cover the bottom, try to corral the fruit towards the center. (You can decide how much of the juice to use—I lost quite a bit that leaked out of the springform.) Set aside to cool while making the cake batter.

For the cake, whisk the all-purpose and rye flours, baking powder, baking soda, and salt in a medium mixing bowl. Place the butter and sugar together in the bowl of a stand mixer fitted with the paddle attachment; cream them together on medium-high speed until the mixture is light and fluffy, approximately 5 minutes. Add the eggs one at a time, mixing for 30 seconds after each, then add the vanilla and mix for another 30 seconds; scrape down the sides and bottom of the bowl with a spatula. The mixture may look curdled at this point, but it will come together in a moment.

Add half of the flour mixture, followed by all of the buttermilk, then the remaining flour, mixing after each addition just until incorporated. (Behold the speckles of rye flour! My mixture looked something like a thick sourdough starter in bread-baking.)

Carefully scrape the batter onto the rhubarb and spread it in an even layer with an offset spatula to the edges of the pan, then smooth the top. Tap the pan gently on the countertop to remove any air bubbles. If you are using a springform pan, place it on a sheet pan to catch any rogue rhubarb juices that escape.

Bake for 30-35 minutes, or until the top of the cake is golden and a toothpick inserted into the center comes out clean. (My cake took 43 minutes, I think due to the thickness of my springform pan and having the sheet pan underneath; in other words, don’t panic if it takes longer.)

Set the cake pan on a wire cooling rack. The recipe says to leave it for only 15 minutes before inverting onto a serving platter, but I found that leaving it for an hour resulted in a prettier, sturdier cake. Peel off the parchment paper and re-position any rhubarb pieces that have become displaced. Cut the cake into wedges and serve warm or at room temperature with fresh whipped cream or ice cream, if desired.