In a skillet, heat the olive oil over medium heat. Add the chopped onions and cook until translucent.
Add the ground beef to the skillet and cook until browned. Drain any excess fat.
Stir in the enchilada sauce, salt, and black pepper. Simmer for a few minutes.
In a baking dish, layer half of the corn tortillas, followed by half of the beef mixture, half of the sour cream, and half of the shredded cheese. Repeat the layers.
Bake in the preheated oven for 20-25 minutes, or until the cheese is melted and bubbly.
Let it cool for a few minutes before serving. Enjoy!
Notes:
This casserole can be made ahead and refrigerated. Just bake it when you're ready to eat.