Mix topping ingredients together; set aside. In a large bowl, combine eggs, sour cream and vanilla, then add to sifted dry ingredients. Grease skillet AFTER heating to 250 degrees. Lightly sprinkle flour over skillet and spread the batter evenly in the pan. Cover, and bake for 50 minutes at 250 degrees, or until 'toothpick' test comes out clean. After baking, spread topping over cake and bake 10 minutes longer.