#### **Step 1: Preheat & Prep**
Preheat oven to **375°F (190°C)** and grease a **9x13-inch baking dish**.
#### **Step 2: Cook the Ground Beef**
In a large skillet over **medium heat**, cook **ground beef and diced onion** until browned. Drain excess grease, then stir in **garlic, salt, black pepper, paprika, and thyme**. Remove from heat.
#### **Step 3: Make the Creamy Sauce**
In a bowl, whisk together **cream of mushroom soup, sour cream, milk, and garlic powder** until smooth.
#### **Step 4: Layer the Casserole**
Arrange **half of the sliced potatoes** in the baking dish.
Spread **half of the cooked beef** over the potatoes.
Pour **half of the creamy sauce** over the beef.
Sprinkle with **half of the cheddar and mozzarella cheese**.
Repeat with the remaining potatoes, beef, sauce, and cheese.
#### **Step 5: Bake the Casserole**
Cover with **foil** and bake for **45 minutes**. Remove foil and bake for an additional **15-20 minutes** until the cheese is golden and bubbly.
#### **Step 6: Rest & Serve**
Let the casserole sit for **5-10 minutes** before serving. Garnish with **fresh parsley or green onions** if desired.