Rhubarb Upside-Down Cake
- 2 1/2 sticks unsalted butter, at room temperature, more to grease pans
- 1 1/2 pounds rhubarb, rinsed and sliced into 1/2-inch cubes about 4 cups
- 2 teaspoons cornstarch
- 1 1/2 cups granulated sugar
- 1/2 cup light brown sugar
- 2 cups cake flour
- 1 1/4 teaspoons baking powder
- 1/2 teaspoon fine sea salt
- Zest of 1 lemon, grated
- 1 teaspoon vanilla extract
- 4 large eggs
- 1/3 cup sour cream
- 2 teaspoons lemon juice
- Heat oven to 325 degrees.
- Line the bottom of a 9-inch springform pan with parchment paper. Butter the paper and sides of the pan. Wrap two layers of foil under the pan, and place it on a buttered baking sheet.
- In a medium bowl, mix rhubarb, cornstarch and 1/2 cup granulated sugar.
- Mix the brown sugar and 1/2 stick butter in a pan over medium heat. Whisk until smooth and bubbling, about 2 minutes.
- Sift together the cake flour, baking powder and salt.
- Whip 2 sticks butter in a mixer with a paddle attachment for 2 minutes. With your fingers, blend the remaining 1 cup sugar with lemon zest until the mixture is uniform in color. Cream together with the butter at medium-high speed until it is light and fluffy, about 4 minutes, stopping to scrape down the bowl halfway through.
- Add the vanilla and mix well.
- Add the eggs, one at a time, mixing well after each addition.
- Mix in the sour cream, then the lemon juice. (It's O.K. if the mixture looks curdled.)
- With the mixer set to low speed, add the flour mixture, 1/4 cup at a time, until well combined. Scrape down the mixer bowl in between the additions.
- Pour the brown-sugar mixture into the cake pan, then spoon in the rhubarb and its juices.
- Spoon in the batter so it covers all of the rhubarb. Smooth out the top.
- Bake for 1 hour and 15 minutes, or until the top of the cake is firm to touch and a toothpick stuck in the middle comes out without any large, moist crumbs.
- Place the pan on a wire rack, and cool for 15 minutes.
- Run a knife around the cake, place a plate on top of the pan and turn it upside-down. Release the cake from the pan while still warm or else it will stick.