Brown the ground beef in a skillet over medium-high heat. Drain off any excess grease.
Stir in the taco seasoning and cook according to package directions.
In a large bowl, combine the cooked ground beef, refried beans, Rotel tomatoes, and sour cream. Mix well.
In a 9×13 inch baking dish, layer half of the tortilla strips.
Spread half of the beef mixture over the tortilla strips.
Sprinkle with half of the cheddar and Monterey Jack cheeses.
Repeat the layers with the remaining tortilla strips, beef mixture, and cheeses.
Bake for 20-25 minutes, or until the cheese is melted and bubbly.
Let stand for 5 minutes before serving. Serve with your favorite toppings.
Notes
For a make-ahead option, assemble the casserole, cover tightly, and refrigerate for up to 24 hours. Bake as directed, adding a few extra minutes if needed.
To freeze, assemble the casserole in a freezer-safe dish, cover tightly with plastic wrap and then foil. Freeze for up to 3 months. Thaw in the refrigerator overnight and bake as directed.
You can adapt this recipe for a slow cooker. Brown the beef and mix with other ingredients. Place tortilla strips in the bottom of the slow cooker, top with the beef mixture, and sprinkle with cheese. Cook on low for 4-6 hours or on high for 2-3 hours.