Preheat oven to 350 degrees F (175 degrees C). In a large bowl, mix flour, 1 tablespoon sugar and baking powder in a bowl. Cut in butter until mixture looks like coarse crumbs. Stir in 2 tablespoons whipping cream and 1 egg. Press in bottom of ungreased 9-inch square pan and arrange plums over the top.
Bake in the preheated oven for 25 to 30 minutes. While cake is baking, in a bowl, combine 1/2 cup whipping cream, 1/2 cup sugar, 1 teaspoon vanilla and 1 egg. Beat well, and pour mixture over plums and bake an additional 20 to 30 minutes or until custard is set. Serve warm or cool. Store in refrigerator.