Rhubarb Strawberry Coffee Cake

In a saucepan, combine rhubarb, cut in 1 inch pieces and add strawberries. Cook, covered, about 5 minutes. Add lemon juice. Combine the sugar and cornstarch. Add to rhubarb mixture. Cook and stir 4 to 5 minutes or until thickened and bubbly. Cool. In mixing bowl, stir together flour, sugar, baking soda, baking powder and salt. Cut in butter or margarine until it resembles fine crumbs. Beat together buttermilk, eggs and vanilla. Add to the dry ingredients. Stir to moisten. Spread half the batter in a greased 13 x 9 x 2 inch pan. Spread the cooled filling over the batter in pan. Spoon remaining batter in small mounds atop the filling. Combine the sugar and flour. Cut in butter or margarine to make fine crumbs. Sprinkle crumbs over the batter in pan. Bake at 350 degrees for 40 to 45 minutes. Serves 12 to 15.