the same skillet, melt butter (or heat oil). Add flour and whisk for 1–2 minutes to form a roux. Gradually whisk in milk until smooth. Season with garlic powder, onion powder, salt, and pepper. Let simmer until slightly thickened.
Step 4: Layer the Casserole
Grease a 9×13-inch baking dish. Layer half of the sliced potatoes on the bottom. Spread half of the cooked beef mixture on top, then pour half the sauce. Sprinkle with 1 cup of cheddar cheese. Repeat layers with remaining potatoes, beef, sauce, and cheese.
