1. Heat oven to 350 F.
2. Coat bottom of 9-inch round cake pan with melted butter and top evenly with brown sugar.
3. Arrange slices of plum to cover pan, very slightly overlapping.
4. Sift together dry ingredients.
5. Beat together wet ingredients in large bowl.
6. Gradually beat together wet and dry ingredients until smooth.
7. Pour mixture over plums.
8. bake for 35 minutes, or until inserted toothpick comes out clean.
9. Cool for 5 minutes, then invert onto plate to serve.