Mix 1 cup of the flour with sugar and yeast. Add warm milk, mix well and let rise for about 30 minutes. Lightly beat eggs and add to dough. Mix in salt, butter and the rest of the flour. Beat dough in bowl for about 5 minutes by hand. Let dough rise, covered by a damp cloth, in a warm place until it has doubled in size. While dough is rising, sauté onions in butter. Lightly beat eggs and add to sour cream. Mix all ingredients for the topping except the ham. Roll out dough like a pizza and place on a large, oiled cookie sheet. Cover with topping, sprinkle with ham. Bake at 400°F for about 40 minutes.