• Heat a skillet over medium-high heat. Add ground beef, onion, and garlic. Cook until a deep brown crust forms and the meat is fully browned. Drain excess fat.
• Melt butter in a saucepan over medium heat. Whisk in flour for 1 minute. Gradually whisk in milk and heavy cream until thick. Remove from heat and stir in 2 cups of the cheddar cheese until smooth.
• Preheat oven to 375°F (190°C). In a greased 9x13 inch ceramic baking dish, layer half the sliced potatoes, half the beef, and half the cheese sauce. Repeat layers.
• Cover tightly with aluminum foil and bake for 45 minutes until the potatoes are tender.
• Remove foil, top with remaining 1 cup of cheddar cheese, and bake uncovered for 20 minutes until the cheese is bubbly and golden-brown with slightly charred crispy edges.
• Let rest for 15 minutes to allow the sauce to set. Scatter finely chopped fresh green parsley evenly over the top before serving.

Notes:

• Ensure potatoes are sliced to an exact 1/8-inch thickness for even baking. Do not skip the covered baking phase; it is crucial for tenderizing the potatoes.