Preheat your oven to 375°F (190°C).

Heat the olive oil in a large oven-safe skillet over medium-high heat. Add the ground beef and cook, breaking it up with a spatula, until browned. Drain off any excess grease.

Add the chopped onion to the skillet and cook until softened, about 5 minutes. Stir in the minced garlic and cook for another minute until fragrant.

Stir in the undrained diced tomatoes, rinsed kidney beans, and drained corn. Add the chili powder, cumin, salt, and pepper. Bring the mixture to a simmer and cook for 5-7 minutes, allowing the flavors to meld.

In a small bowl, whisk together the sour cream and milk until smooth. Pour this mixture over the beef and vegetable mixture in the skillet and stir gently to combine.

Sprinkle 3/4 cup of the shredded cheddar cheese evenly over the top of the casserole.

Transfer the skillet to the preheated oven and bake for 20-25 minutes, or until the casserole is heated through and the cheese is melted and bubbly.

Remove from the oven, sprinkle with the remaining 1/4 cup of cheddar cheese, and let it rest for a few minutes before serving. If desired, top with crushed tortilla chips.