In a medium skillet, saute the onions in butter over low heat until they just begin to brown, about 15 minutes.
Season with ΒΌ teaspoon of the salt, the marjoram, and the pepper. Set aside to cool. Preheat oven to 450 degrees.
In a food processor bowl place flour, cornstarch, baking powder, and the remaining salt, mix. Add the shortening and process just until it is the texture of soft crumbs. Add the milk and mix quickly to form a soft dough.
Oil a 10-inch round cake pan and lightly use your fingers to spread the dough out evenly. Spread the cooked onion over the top.
Beat the egg and sour cream together. Spoon the mixture over the onion, and spread it out to the very edge of the pan.
Sprinkle lightly with poppy seeds and paprika.
Bake for 20 minutes. Let cool slightly, then cut into wedges.