Step 1

Thaw 2 cups frozen corn kernels at room temperature (1 to 2 hours) or according to package instructions.

Step 2

Arrange a rack in the middle of the oven and heat the oven to 400ºF. Meanwhile, dice 1 medium yellow onion and mince 2 garlic cloves. Grate 8 ounces sharp cheddar cheese (about 2 cups) on the large holes of a box grater. Drain and rinse 1 (about 15-ounce) can black beans.

Step 3

Heat 2 tablespoons olive oil in a large skillet over medium-high heat until shimmering. Add 1 pound lean ground beef, season with 1 teaspoon kosher salt and 1/4 teaspoon black pepper, and cook, breaking up the meat with a wooden spoon, until browned and cooked through, 6 to 8 minutes. Add the onion, garlic, and 1 (1-ounce) packet taco seasoning mix. Cook, stirring occasionally, until the onion is softened, about 3 minutes.

Step 4

Remove from the heat. Add 1 (14.5-ounce) can fire-roasted diced tomatoes with juices and 1 cup sour cream, and stir to combine.

Step 5

Transfer the beef mixture to a 9x13-inch baking dish and spread into an even layer. Sprinkle evenly with the corn and black beans. Sprinkle with half of the cheese. Arrange 32 ounces tater tots in a single tight, even layer on top of the cheese.

Step 6

Bake until the tater tots are golden brown and the casserole is bubbling, about 35 minutes. Sprinkle with the remaining cheese and bake until melted, about 5 minutes more.