Step 1: Preheat the Oven

Preheat oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish with butter or nonstick spray.

Step 2: Cook the Ground Beef

Heat olive oil in a large skillet over medium-high heat.
Add ground beef and cook until browned.

Add chopped onion and minced garlic and cook for about 5 minutes, until softened.

Season with salt, pepper, paprika, thyme, and Worcestershire sauce.

Drain excess grease if necessary.

Step 3: Make the Creamy Beef Sauce

Sprinkle flour over the beef mixture and stir well.

Gradually pour in beef broth, whisking to prevent lumps.

Add milk and cook for about 5 minutes, stirring frequently, until the sauce thickens into a creamy consistency.

Taste and adjust seasoning if needed.

Step 4: Prepare the Potatoes

Wash and peel potatoes (optional).
Slice them thinly (about ⅛ inch thick) using a sharp knife or mandoline.

Rinse briefly under cold water to remove excess starch and pat dry.

Step 5: Assemble the Casserole

Layer half of the sliced potatoes in the baking dish.

Spread half of the beef mixture over the potatoes.

Sprinkle 1 cup cheddar cheese.

Add another layer of potatoes.

Spread the remaining beef mixture.

Top with the remaining cheddar and mozzarella cheese.

Dot the top with small pieces of butter.

Step 6: Bake

Cover with aluminum foil and bake for 45 minutes.

Remove foil and bake an additional 15–20 minutes, until potatoes are tender and the cheese is golden and bubbly.

Optional: Broil for 2–3 minutes for a crispier cheese topping.

Step 7: Rest and Serve

Let the casserole rest for 10 minutes before slicing.

Garnish with fresh parsley and paprika, then serve warm.