Preheat your oven to 375°F (190°C). Grease a 9x13 inch baking dish or a deep casserole dish.
In a skillet over medium heat, cook the ground beef with diced onions and garlic. Season with salt, pepper, and paprika. Cook until browned. Drain any excess fat.
In a bowl, combine cream of mushroom soup and milk. Mix until smooth.
Start by layering half the sliced potatoes in the bottom of the dish. Spread half of the beef mixture over the potatoes. Pour a third of the soup mixture on top.
Repeat with remaining potatoes and beef. Pour remaining soup mixture evenly over the top. Dot with butter pieces. Cover tightly with foil.
Bake covered for 45 minutes, until potatoes are tender.
Remove foil, top with shredded cheddar, and bake uncovered for another 15 minutes, until cheese is bubbly and slightly golden.
Let it rest for 5–10 minutes before serving. Garnish with parsley or chives if desired.
Notes
Slice potatoes evenly so they cook uniformly. A mandoline slicer is helpful. Add a can of drained corn or green beans between layers for added veggies. For a crispier top, broil for the last 2–3 minutes.