Upside-Down Rhubarb Cake
In this flourless upside-down cake, resist the temptation to add berries or other fruit. The flavorful, bright liveliness of the rhubarb is front and center, its sourness mellowed just slightly with vanilla and butter. The base of the cake, made entirely of almond meal, whispers of cardamom. To my palate, the combination delights, and I often find myself eating this cake for breakfast the next day with a good cup of coffee.
Serves 8 | start to finish 60–70 minutes
4 tablespoons butter
4 cups rhubarb, cut into 1/2-inch cubes (about 1 1/4 lb.)
1 1/4 cups sugar, divided
1 tablespoon fresh lemon juice
2 teaspoons vanilla extract
pinch of salt
4 eggs, separated into yolks and whites, at room temperature
zest from one lemon
1/4 teaspoon cardamom
1 1/2 cups finely ground almond flour or meal
1 teaspoon baking powder
1 teaspoon white or cider vinegar
Powdered sugar for sprinkling
Preheat oven to 375°F
Over medium heat, melt butter in a 9-inch cast-iron skillet and brush the skillet’s sides with it. Add rhubarb, 3/4 cup sugar, lemon juice, vanilla extract, and pinch of salt, and stir for 2 minutes, just until combined and sugar has dissolved. Turn heat off. Do not continue to cook the rhubarb. You can either bake the cake in the same skillet or transfer the rhubarb mixture to a parchment-lined and buttered 9-inch springform pan.
In a medium bowl, whisk egg yolks with lemon zest, cardamom, and 1/4 cup sugar until creamy and sugar has dissolved. Set aside. In a small bowl, whisk almond flour, pinch of salt, and baking powder until combined.
Add flour mixture to egg mixture and stir to incorporate. You will have a very thick, heavy batter at this point.
In a stand mixer, whip egg whites on medium-high speed, and once you see bubbles, add a pinch of salt and the vinegar. Whip until the egg whites have formed soft peaks, then add the remaining 1/4 cup sugar a little at a time, whipping until medium-stiff peaks form. Turn the mixer speed down to medium-low and begin spooning in the flour/egg yolk batter, a heaping spoonful at a time, until it is all combined, scraping down the sides as necessary.
Pour batter over the rhubarb in the skillet (or the springform pan) and place in a preheated oven for 30 minutes. While it is baking, prepare what you plan to flip the cake onto. At 30 minutes, check for doneness by inserting a toothpick or skewer into the middle of the cake. If the toothpick comes out clean, the cake is done. If not, bake a bit longer. Pull from the oven and immediately place a cake platter or cake stand over the skillet and invert, gently tapping the bottom of the skillet so it releases. (Note: If using a springform pan, let the cake cool before removing the pan sides and flipping.) Let cool 10 minutes before serving. Serve with vanilla ice cream or on its own. The cake is especially good the next day.
gluten free • vegetarian