Heat 2 tablespoons of olive oil in a large skillet over medium heat.

Add the thinly sliced onions and sprinkle with 1 teaspoon of sugar. This helps them caramelize faster and enhances their natural sweetness.

Stir the onions occasionally for about 20–25 minutes, until they’re deep golden brown and soft. Don’t rush this step—it’s what gives the casserole its rich flavor.

Pro Tip: If the onions start sticking or browning too fast, reduce the heat slightly and add a splash of water to loosen things up.

While the onions are cooking, season the chicken pieces with garlic powder, onion powder, salt, and pepper.

In a separate skillet (or once the onions are done and removed), add a light drizzle of oil and cook the chicken over medium-high heat until golden and fully cooked, about 5–7 minutes.

Set aside.

Pro Tip: Don’t overcrowd the pan—cook the chicken in batches if needed so it browns instead of steams.

In a medium saucepan, melt 1 tablespoon of butter over medium heat.

Add 2 tablespoons of flour and whisk constantly for about 1 minute to cook off the raw taste.

Gradually pour in the beef broth while whisking to avoid lumps. Then slowly whisk in the heavy cream.

Stir in thyme and Worcestershire sauce. Let it simmer for 3–4 minutes until slightly thickened.

Pro Tip: Whisk continuously to prevent lumps and ensure a smooth, velvety sauce.

Preheat your oven to 375°F (190°C).

In a 9x13 casserole dish, spread the cooked chicken evenly across the bottom.

Pour the sauce over the chicken, then layer the caramelized onions on top.

Sprinkle the mozzarella and Gruyère (or Swiss) cheese evenly across the top.

Bake uncovered for 20–25 minutes, or until the cheese is melted and bubbly.

In the last 5 minutes, sprinkle the French fried onions on top and return to the oven to crisp up.

Pro Tip: If your cheese isn’t browning enough, switch to broil for the last 2 minutes—but watch it closely!