Make a taco bowl using the underside of a muffin tin. Place the corn tortillas on the underside of the muffin tin and heat in the oven for 15 minutes at 375°F. In a large skillet, brown ground beef and add taco seasoning according to package directions. Place corn tortilla bowl on a plate. Fill with desired amount of shredded lettuce. Top with seasoned ground beef mixture and lettuce, cheese, tomatoes, and sour cream. Serve immediately and enjoy!