Plum Blueberry Upside-Down Cake

Step 1
Preheat the oven to 350 degrees F (175 degrees C). Grease a 9-inch cake pan. Combine flour, baking powder, and salt; set aside.

Step 2
Combine brown sugar and 3 tablespoons butter in the prepared pan. Place pan inside the preheated oven until butter melts and begins to bubble; set aside.

Step 3
Beat 1 cup white sugar and 1/3 cup butter in a large bowl with an electric mixer until light and fluffy. Beat in egg, then stir in vanilla. Beat in flour mixture, alternately with milk, mixing just until incorporated.

Step 4
Arrange plums around the edges of the prepared pan, overlapping slightly. Distribute blueberries in the center. Pour batter into prepared pan, covering fruit completely.

Step 5
Bake in the preheated oven for 40 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool 15 minutes before serving.