In a mixing bowl, cream butter and sugar. Beat in eggs, milk, and vanilla. Stir in squash (mixture will be thin). Pour into a greased 11x7 inch baking pan. Bake, uncovered, at 350 degrees F for 45 minutes or until almost set. Combine topping ingredients; sprinkle over casserole. Return to the oven for 5-10 minutes or until bubbly.