Preheat oven to 375°F (190°C). Grease a 9×13-inch (23×33 cm) baking dish with butter or nonstick spray. Slice potatoes thinly using a mandoline or sharp knife for even cooking.

In a large skillet over medium-high heat, cook ground beef until browned and no longer pink, breaking it up with a spatula.

Add chopped onion and cook for 4 to 5 minutes until translucent and soft. Stir in garlic, salt, pepper, and paprika and cook for 30 seconds until fragrant.

Pour in beef broth and Worcestershire sauce and simmer for 2 to 3 minutes until slightly reduced. The mixture should be moist but not soupy.

In a small bowl, whisk together milk, melted butter, and flour until smooth. This helps the top layer thicken slightly. Reserve 1/2 cup of shredded cheddar for the topping and stir the rest into the milk mixture.

Arrange half of the potato slices in an even layer on the bottom of the prepared dish, overlapping slightly.

Spoon the cooked beef mixture evenly over the potatoes.

Add a second layer of potato slices to cover the beef, pressing gently to compact.

Pour the milk and cheese mixture evenly over the top layer. Sprinkle the reserved 1/2 cup cheddar over the top.

Cover tightly with foil and bake at 375°F (190°C) for 35 minutes. Remove foil and continue baking for 10 to 20 minutes more until the top is golden and the potatoes are tender when pierced with a knife.

Let the casserole rest for 5 to 10 minutes before slicing. This helps it set and makes serving easier.