In a large skillet, heat olive oil over medium-high heat. Add the chicken breasts and cook for about 5-7 minutes on each side, or until golden brown and cooked through. Remove the chicken from the skillet and set aside.

Make the Mushroom Sauce

Sauté the Vegetables

In the same skillet, add the sliced mushrooms, minced shallots, and minced garlic. Sauté for about 5 minutes until the mushrooms are browned and the shallots are translucent.

Deglaze the Pan

Pour in the Madeira wine, scraping the bottom of the pan to release any browned bits. Let it simmer for about 3 minutes.

Add Broth and Cream

Add the beef or chicken broth and heavy cream to the skillet. Stir in the fresh thyme leaves. Let the sauce simmer for another 5-7 minutes until it thickens slightly.

Combine and Bake

Combine Chicken and Sauce

Return the seared chicken breasts to the skillet, spooning the mushroom sauce over the top to coat.

Add Cheese

Sprinkle the shredded Fontina cheese evenly over the chicken and sauce.

Bake

Transfer the skillet to a preheated oven at 375°F (190°C) and bake for about 15-20 minutes, or until the cheese is melted and bubbly.