In a heavy skillet, warm butter and oil over medium heat. If the tamales are
fairly dry, use about a tablespoon more of oil. Add onion and sauté until very soft.
Add tamale pieces and stir them in gently. Cover the skillet for 2 to 3 minutes
to let the mixture steam and heat through, developing a little crust on a few pieces.
Keep the mixture warm while preparing the eggs either sunny-side up or scrambled.
Spoon the tamale mixture onto plates. Arrange an egg over each and add a generous
amount of sauce. Top with the tomato, scallions, crema and cheese.