In a heavy skillet, cook the onion in 2 Tbsp lard, over mod-low heat, stirring, until it is golden. Stir in the cayenne and salt and pepper to taste. Reserve the mixture.
Onto a sheet of wax paper, sift together the flour, baking powder, and salt. Sift the mixture again into a bowl. Add the remaining lard, and blend the mixture until it resembles fine meal. Stir in the milk, stirring until the dough is combined well. Turn out onto a floured surface and knead it for 30 seconds. Pat into a 9-inch square, press it evenly into a greased 9-inch baking pan and top with the onion mixture.
In a small bowl, whisk together the egg, sour cream, and salt and pepper to taste. Pour this over the onion mixture, using a spatula to cover the onion mixture evenly.
Bake in the middle of a preheated 450f oven for 20-25 minutes or until it is cooked through. Cut into squares and serve hot.
A 1943 Gourmet Mag. favorite