Step 1: In a large skillet or Dutch oven, cook the ground beef over medium-high heat, breaking it up with a spoon, until fully browned. Drain off any excess fat.
Step 2: Add the chopped onion and minced garlic to the skillet with the beef. Cook for 5-7 minutes, or until the onion is softened and translucent and the garlic is fragrant.
Step 3: Stir in the diced tomatoes (undrained), tomato sauce, corn, kidney beans (rinsed and drained), and pinto beans (rinsed and drained). Add the chili powder, cumin, smoked paprika, salt, and black pepper. Bring the mixture to a simmer, then reduce heat and let it cook for 10 minutes, allowing the flavors to meld.
Step 4: Preheat your oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish. Pour the beef and bean mixture into the prepared dish, spreading it evenly.
Step 5: In a medium bowl, combine the cream of mushroom soup, milk, and sour cream. Whisk until smooth. Gently spread this creamy layer over the beef and bean mixture.
Step 6: Sprinkle the shredded cheddar cheese evenly over the creamy layer.
Step 7: Bake in the preheated oven for 25-30 minutes, or until the casserole is bubbling around the edges and the cheese is melted and golden brown. Let the casserole stand for 5-10 minutes before serving.