Strawberry-Rhubarb Sourdough Coffee Cake

FOR THE FILLING:
In a medium saucepan combine strawberries, rhubarb, and water. Bring to boiling; reduce heat. Cover and simmer for 5 minutes. Combine granulated sugar and cornstarch; stir into fruit mixture. Cook and stir till thickened and bubbly. Remove from heat; set aside.

FOR THE TOPPING:
In a small mixing bowl mix oats, brown sugar, nuts, and flour. With a pastry cutter, cut in butter or margarine till mixture resembles coarse crumbs. Set aside.

FOR THE DOUGH:
In a medium mixing bowl stir together flour, granulated sugar, baking powder, baking soda, and salt. With a pastry cutter, cut in butter or margarine till mixture resembles fine crumbs. Mix sourdough starter, egg, and vanilla; add to flour mixture. Stir just till moistened. Spread half of the batter in a greased 9 by 9 by 2-inch baking pan. Spread filling on top of dough. Drop remaining dough in small mounds over filling. Sprinkle topping over batter. Bake in a preheated 350 degrees F oven for 35 to 40 minutes, or till golden brown. Serve warm.