Cream butter with sugar in small bowl until smoothly blended.
Add eggs, one at a time, beating well after each addition.
Stir in almond extract and flour; mix well, Spread batter evenly in buttered floured 10-inch round pan.
Cut plums in half and remove pits; arrange halves, cut side up, over batter.
Sprinkle plums with additional sugar.
Bake at 375 degrees for 40 minutes; cool for 30 minutes before serving.
Sprinkle with confectioners' sugar.