Prepare the Meat Sauce

• Add 2 tablespoons butter to a large pan over low-medium heat. Add diced onions and sauté for about 4 minutes.

• Increase heat to medium, add mushrooms and the remaining butter. Sprinkle with salt and cook for 6–7 minutes until the mushrooms release and reduce their moisture.

• Add ground beef along with onion powder, celery salt, garlic powder, black pepper, and bouillon cube. Cook until no longer pink.

• Stir in the flour and cook for 1–2 minutes to thicken.

• Add chicken stock, ketchup, and ½ cup of heavy cream. Reduce heat and simmer for 15 minutes, stirring occasionally.

2. Prepare the Potatoes

• Peel and slice the potatoes to ⅓-inch thickness.

• Parboil in salted water until just tender enough for a knife to pierce but not fully cooked. Drain and set aside.

3. Assemble the Casserole

• Preheat oven to 350°F and generously butter a 9×13-inch baking dish.

• Layer half the sliced potatoes on the bottom of the dish.

• Spread half of the beef mixture, then sprinkle with half of the cheese.

• Add another layer of potatoes, the remaining beef mixture, and top with the rest of the cheese.

4. Bake

• Cover with non-stick foil and bake for 30 minutes.

• Remove foil and bake uncovered for an additional 30 minutes, until golden brown and bubbly.