Preheat the oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish.
Dice 1 medium white onion.
In a large skillet over medium-high heat, melt 2 tablespoons salted butter. Add in the diced onion and cook until softened and lightly browned, about 3 to 5 minutes.
Add 1 1/2 pounds ground beef, 1 (7 ounce can) diced green chiles, 1 tablespoon ground cumin, 2 teaspoons salt, 2 teaspoons chili powder, and 2 teaspoons garlic powder. Cook, stirring occasionally, until the beef is browned and fully cooked, about 6 to 8 minutes. Remove from heat.
In a medium skillet over medium heat, add 1/4 to 1/2 teaspoon olive oil. Working one at a time, brown all 12 (6-inch) corn tortillas until lightly golden, about 1 minute per side, adding more oil as needed. Once browned, cut each tortilla in half, giving you 24 halves. You'll use half of them (12 halves) for the bottom layer and the remaining halves for the middle layer of the casserole.
Arrange half of the tortilla halves in the bottom of the prepared baking dish. Sprinkle with 1 cup shredded cheddar cheese. Spread half of the ground beef mixture over the cheese.
Evenly layer the drained 1 (14.5 ounce can) black beans over the beef. Spoon 1 cup salsa over the beans. Arrange the remaining tortilla halves on top.
Spread the remaining ground beef mixture over the tortillas. Spoon 2 cups corn kernels evenly on top, followed by the remaining 1 cup salsa. Sprinkle with the remaining 2 cups shredded cheddar cheese.
Bake, uncovered, for 25 to 30 minutes, until bubbly and the cheese is golden brown.
Let cool slightly before serving. Add toppings as desired.
Video
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Notes
Toppings are optional, but here are some great ideas: