01 -
Preheat oven to 180°C (350°F).
02 -
Grease the sides of a 33cm x 23cm (13-inch x 9-inch) baking pan. Pour the melted butter into the bottom of the pan and sprinkle brown sugar evenly over it.
03 -
Arrange strawberry slices on the brown sugar layer, then sprinkle rhubarb pieces evenly over the strawberries. Gently press the fruit into the brown sugar mixture.
04 -
In a large bowl with a hand mixer or in a stand mixer with paddle attachment, cream butter and both sugars until well combined. Beat in egg, egg yolk, and vanilla until completely incorporated.
05 -
In a separate bowl, whisk together flour, baking soda, and baking powder.
06 -
Alternately add the dry mixture and sour cream to the butter mixture on low speed. Mix for an additional minute to ensure thorough combination.
07 -
Fold in the finely chopped rhubarb until evenly distributed throughout the batter.
08 -
Drop spoonfuls of batter over the fruit layer and carefully spread into an even layer, being careful not to disturb the fruit underneath.
09 -
Bake until golden brown and a toothpick inserted in the center comes out clean, about 50 minutes. If the top browns too quickly, cover loosely with aluminum foil.
10 -
Remove from oven and allow to cool for 20 minutes. Run a butter knife around the edges to loosen the cake.
11 -
Place a large serving platter over the pan and carefully flip to invert the cake. The fruit topping will now be on top with the cake underneath.
12 -
Slice and serve while still warm or at room temperature.