Begin by preheating the oven and greasing a large baking dish to ensure nothing sticks during the baking process.

In a large skillet, brown the ground beef with the sliced onions in olive oil until the meat is fully cooked and the onions are soft.

Stir the Worcestershire sauce into the meat mixture to add depth and flavor before setting the skillet aside.

Melt the butter in a saucepan and whisk in the flour to create a smooth roux, cooking it briefly to remove the raw flour taste.

Gradually pour in the milk and half and half, whisking constantly until the mixture thickens into a creamy sauce.

Season the sauce with garlic powder and salt, then stir in most of the shredded cheese until it is completely melted.

Create layers in the baking dish by starting with sliced potatoes, followed by the beef mixture and a generous pour of cheese sauce.

Repeat the layers until all ingredients are used, finishing with a final layer of cheese sauce and a sprinkle of the remaining cheddar.

Lightly dust the top with paprika and cover the dish tightly with foil before placing it in the oven.

Bake the covered casserole until the potatoes are steaming, then remove the foil and continue baking until the top is golden and bubbling.

Allow the dish to rest for a few minutes before slicing to let the sauce thicken and set.