Set the oven to preheat at 350°F.

In a skillet set over medium heat, begin cooking the ground beef. Introduce the chopped onions and minced garlic, stirring and sautéing until the beef is thoroughly browned. Drain any residual fat, if present.

In a separate bowl, blend the condensed mushroom soup with milk and incorporate 1 cup of shredded cheddar cheese.

Coat a 2-quart (11x7 inch) baking dish lightly with non-stick cooking spray. Begin layering by arranging half of the sliced potatoes across the bottom. Spoon over half the prepared soup mixture, then spread half the cooked beef. Repeat the layering sequence with the remaining potatoes, soup, and beef.

Cover the assembled dish with aluminum foil and bake for 60 minutes.

Remove the foil and distribute the remaining 1 cup of cheddar cheese over the top. Return the dish to the oven and bake, uncovered, for an additional 15 to 20 minutes, or until the cheese is melted and bubbly and the potatoes are fork-tender.

Once baked, allow the casserole to rest for 10 to 15 minutes before slicing and serving.