Plum Streusel Cake - Pauline

1/4 cup margarine 3/4 cup sugar 2 eggs, separated 1 1/2 cups all purpose flour 1 tsp. baking powder 1/2 cup 2% milk 2 cans (14 oz/398 ml) plums - or 2 cups halved ripe plums Streusel Topping: 1/2 cup packed brown sugar 1 Tbsp. soft margarine 1 tsp. cinnamon Glaze: 1/4 cup icing sugar 1 tsp. 2% milk 1/4 tsp. vanilla or almond essence Cream margarine, sugar and egg yolks till fluffy. Combine flour and baking powder, beat into egg mixture alternately with milk. Beat egg whites till stiff and fold into batter. Turn into a greased 9"x9" pan. Arrange pitted, halved plums over top. Combine streusel topping and sprinkle over fruit. Bake 350 degrees for 35 to 45 mins. Drizzle glaze over cooled cake.