The sweet plum topping cooks down while baking and settles nicely into the tender butter cake. When the cake is inverted, you have a showpiece dessert with luscious fruit oozing over the top and dripping down the sides.

Upside-Down Plum Cake

Separate yolks and whites from eggs.  Allow eggs to stand at room temperature for 30 minutes.

Preheat oven to 350 degrees. Spray bottom and sides of a 9-inch-round baking pan with nonstick spray. Line with parchment paper; spray paper with nonstick spray and coat with flour; set aside.

Halve plums crosswise; remove stones. Cut plums into thin slices; set aside.

In a small saucepan, melt 4 tablespoons butter over medium heat. Add 1/2 cup sugar and jam. Cook over medium-low heat for 2 minutes or until thickened. Pour into prepared baking pan. Arrange plum slices in a single layer on top.

In a medium bowl, whisk together flour, baking powder and salt; set aside.

In a large mixing bowl, beat remaining 1/2 cup butter at medium speed of an electric mixer for 30 seconds. Add 1 cup sugar; beat until light and fluffy. Beat in egg yolks, vanilla and orange zest, scraping sides of bowl.

Alternately add flour mixture and heavy whipping cream to butter mixture, beating on low after each addition, just until combined; set aside.

Using thoroughly cleaned beaters, beat egg whites until soft peaks form (tips curl). Add remaining 2 tablespoons sugar, 1 tablespoon at a time. Continue beating until stiff peaks form (tips stand straight). Fold beaten whites into cake batter. Spoon batter over plums in pan; spread evenly. 

Bake about 45 minutes or until a toothpick inserted near center comes out clean. Cool in pan on wire rack for 2 minutes.

Using a small sharp knife, loosen cake around edge of pan. Invert cake onto a serving plate. Remove and discard parchment paper. Serve cake warm topped with sweetened whipped cream, if desired.