Creating this delicious Beef and Potato Casserole is a straightforward process. Follow these step-by-step instructions, and you’ll have a delectable dish ready in no time.

Step 1: Prepare the Ingredients

1. Preheat your oven to 375°F (190°C).
2. Wash and peel the potatoes. Slice them into thin rounds, about 1/4 inch thick.
3. Dice the onion and mince the garlic.

Step 2: Cook the Ground Beef

1. Heat olive oil in a large skillet over medium heat.
2. Add the diced onion and garlic, sauté until softened.
3. Add the ground beef to the skillet, cooking until browned. Break it into crumbles as it cooks.
4. Drain excess fat if necessary.
5. Season with salt, pepper, paprika, and thyme. Stir well and remove from heat.

Step 3: Make the Creamy Sauce

1. In a separate saucepan, melt butter over medium heat.
2. Add flour to the melted butter, whisking continuously to form a roux. Cook for about 1 minute.
3. Gradually add milk, whisking constantly to avoid lumps, until the mixture thickens.
4. Stir in shredded cheese and mustard powder until the cheese melts and the sauce is smooth.

Step 4: Assemble the Casserole

1. In a greased 9×13-inch baking dish, layer half of the sliced potatoes on the bottom.
2. Spread half of the cooked beef mixture over the potatoes.
3. Pour half of the creamy sauce over the beef and potatoes.
4. Repeat the layers with the remaining potatoes, beef, and sauce.

Step 5: Bake the Casserole

1. Cover the baking dish with foil and bake in the preheated oven for 45 minutes.
2. Remove the foil and bake for an additional 15 minutes, or until the top is golden and bubbly.
3. Check the tenderness of the potatoes with a fork.

Step 6: Rest and Serve

1. Allow the casserole to rest for 10 minutes before serving. This helps the layers set.
2. Garnish with fresh herbs like parsley or chives if desired.