Preheat oven to 350 degrees. Chop enough plums to get 1 1/2 cups. Combine chopped plums with 1/4 cup sugar and the cornstarch. Cream butter with remaining 3/4 cup sugar. Beat in eggs, milk, flour, baking powder, salt and cinnamon until well combined. Pour half the batter into greased and floured 8-inch springform pan. Spoon on plum mixture. Spread remaining batter over plums to cover. Combine 2 tablespoons sugar and 1/4 teaspoon cinnamon and sprinkle on the cake. Bake 40 minutes and then cover top loosely with foil. Continue baking 20 minutes until toothpick inserted into center comes out clean. Cool partially. Remove pan sides. Place on plate and cut into wedges to serve. Best served warm or at room temperature. -----