Preheat oven to 400Â°F.
Grease 9-inch-round pan.
Cream butter and 1/2 cup sugar until light and fluffy.
Beat in eggs one at a time; add flavorings, beat well.
Sift flour, baking powder, and salt together; blend in.
Pour batter into pan.
Arrange plum halves in batter, cut side down.
Mix together topping ingredients; sprinkle over plums and batter.
Bake 30 minutes.