For ground beef: In a skillet, heat oil over medium high heat. Add onions, sauté until light and translucent, about 3 minutes. Add tomatoes, garlic cloves and serrano chile. Continue cooking for an additional 3 minutes, stirring occasionally. Add ground beef, breaking up with a spoon. Cook until beef is no longer pink and fully cooked. Reduce heat to low. Add salt, pepper, chili powder, cumin, and oregano stir to combine and allow to simmer for 5 minutes.
For puffy tacos: In a bowl combine the masa harina and salt. Slowly add the warm water while mixing until a smooth dough forms, adding more warm water if needed. Pull off pieces of dough and roll them into small balls, place on baking sheet covered with damp towel. In a Dutch oven or large saucepan heat 2 inches of vegetable oil to 350 degrees.
serves 8