Heat oven to 350 degrees.

Cream the sugar and butter in a bowl. Add the flour, baking powder, salt and eggs and beat well.

Spoon the batter into a spring form of 8, 9 or 10 inches. Place the plum halves skin side up on top of the batter. Sprinkle lightly with sugar and lemon juice, depending on the sweetness of the fruit. Sprinkle with (about) 1 teaspoon of cinnamon, depending on how much you like cinnamon.

Bake one hour, approximately. Remove and cool; refrigerate or freeze if desired. Or cool to lukewarm and serve plain or with whipped cream.