Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish with olive oil or butter.

In a large skillet, over medium heat, brown the ground beef or turkey for about 7-10 minutes, then drain excess fat.

Add finely chopped onion and minced garlic to the cooked meat, sauté for 2-3 minutes until onions are translucent.

In a mixing bowl, combine cream of mushroom soup with milk until smooth, then stir into the beef mixture.

Thinly slice russet potatoes to about 1/8 inch thick and arrange the slices in a plate.

Layer the casserole by placing a bottom layer of potatoes, half the beef mixture, and cheddar cheese. Repeat the layers, finishing with potatoes topped with sauce and cheese.

Cover with aluminum foil and bake for 60 minutes. Remove foil for the last 15-20 minutes for a bubbly cheese topping.

Let the casserole rest for 5 minutes, then serve warm.