Prep: Preheat the oven to 375°F, thinly slice the potatoes, dice the onion and garlic, and shred both cheeses.
Cook the ground beef in a skillet over medium heat until browned, then add the onion and garlic and cook until soft.
Stir in salt and any optional seasonings, then remove from heat.
Spread the beef mixture evenly into a baking dish.
Sprinkle half of the shredded cheddar (mild and sharp mixed) over the beef.
Layer the sliced potatoes over the cheese in slightly overlapping rows.
Top with the remaining cheddar cheese.
Cover tightly with foil and bake for 45 minutes, then uncover and continue baking for 10–15 minutes until the potatoes are fully tender.
Broil for 2–3 minutes at the end if needed to brown the cheese.
Let rest for 10 minutes before serving and top with crumbled bacon if using.