Step 1: Preheat the Oven
Set your oven to 375°F (190°C). Lightly grease a 9-by-9-inch baking dish with butter or cooking spray and set aside.
Step 2: Cook the Beef
Heat the olive oil or butter in a large skillet over medium heat. Add the ground beef and cook for 5 to 7 minutes, breaking it apart as it browns, until no pink remains. Drain any excess fat from the pan. Season the beef with the salt, pepper, and paprika and stir to combine. Remove the beef from the skillet and set aside.
Step 3: Sauté the Vegetables
In the same skillet over medium heat, add the diced onion and minced garlic. Cook for 2 to 3 minutes until the onion is softened and translucent. Add the sliced mushrooms and cook for 5 to 7 minutes, stirring occasionally, until the mushrooms have softened and released their moisture — continue cooking until that moisture has fully evaporated. This step is important: mushrooms that still hold water will make the finished bake watery rather than creamy and cohesive. Add the dried thyme and chili flakes if using, stir to combine, and remove from heat.
Step 4: Prepare the Creamy Mixture
In a medium bowl, whisk together the sour cream and heavy cream until completely smooth. Stir in half of the shredded mozzarella until evenly combined. The mixture should be thick, creamy, and uniform.
