I started out with a grander vision of pureeing strawberries into the batter and doing a layer cake with rhubarb and cream cheese frosting, but given how fresh and beautiful both the strawberries and rhubarb were, it seemed criminal to molest the fruit like that. That's why I turned to an old favorite for integrating fruit into a cake: upside-down cake.
For me, the whole point of an upside-down cake is the jammy fruit and sauce that drizzles down the sides of the inverted cake. That's why I like to make my upside-down cakes with a ton of fruit relative to the batter. There's still plenty of soft buttery cake, as well as the gooey layer between the cake and fruit, but a good third of the height is a layer of fresh fruit glazed in its own juices.
Rather than make a more traditional caramel sauce, I decided to go for simplicity, tossing the fruit in sugar and a bit of starch before lining the bottom of a pan with the fruit. The starch helps thicken the juice released by the rhubarb and strawberries, turning it into a shiny glaze. For the cake, I went with a sweet buttery poundcake batter to balance out the tart fruit.
The result not only looked fantastic, it tasted marvelous too.
- Move the oven rack to the middle position and preheat to 350 degrees F (175 C).
- Toss the strawberries, rhubarb, 1/2 cup of sugar and potato starch together in a bowl.
- Arrange the strawberries along the bottom of a non-stick 9" round or 8-inch square pan so that the cut sides face down. Top with the rhubarb and any remaining liquid, using the rhubarb to fill in the gaps between the strawberries.
- Whisk together the flour, baking soda, and salt.
- In the bowl of al electric mixer, whisk the butter and 3/4 cup sugar together until light and fluffy ( about 2 minutes).
- Add the eggs one at time and continue whisking until fully incorporated.
- Add the yogurt and vanilla extract and whisk to combine.
- Switch to the beater attachment and add the flour mixture in three additions beating on low speed until just combined after each addition.
- Spread the batter over the fruit and put the pan in the oven.
- Bake until a toothpick inserted into the middle of the cake comes out without any batter on it (30-40 minutes).
- Let the cake cool for 20 minutes. Run a knife along the edges if need be and then invert onto a large plate. If some of the fruit remains stuck to the pan, just stick them back into the cake.