In a large skillet, cook onions in 1/2 cup butter over low heat for 10 minutes. Stir in the poppy seeds, salt, paprika and pepper; cook until golden brown, stirring occasionally. Remove from heat; set aside.

In a large bowl, combine flour, cornstarch, baking powder and sugars. Cut in 1-1/4 cups butter until mixture resembles coarse crumbs.

Melt the remaining butter. In a bowl, whisk the eggs, milk, sour cream and melted butter.

Make a well in the dry ingredients; stir in egg mixture just until moistened. Spread into a greased 10 inch springform pan. Spoon onion mixture over the dough. Place pan on baking sheet. Bake at 350 º for 35 to 45 minutes or until toothpick inserted near the center comes out clean. Serve warm. Yield: 10-12 servings.