In a large pot, melt 2 tablespoons of butter over high heat. Add the chicken thighs, seasoning lightly with salt and pepper. Cook for about 1.5 minutes until golden, then turn them over, seasoning again. Cook for an additional minute. Remove the chicken from the pot and let it rest for 5 minutes before chopping into small pieces.

Preheat your oven to 160°C / 325°F. In the same pot, melt 4 tablespoons of butter over high heat and add the sliced mushrooms. Sauté for around 4 minutes until the mushrooms start to soften.

Incorporate the minced garlic and chopped onion into the pot. Cook for another 3 minutes until the onions become translucent.

Lower your heat to medium and sprinkle the flour over the mushroom mixture. Stir for about 30 seconds. Slowly add in the milk, stirring continuously until the mix thickens.

Gradually add the chicken stock, cream, salt, and black pepper. Stir until well combined and let the sauce heat through until it thickens.

Stir in half of your cheese until melted. Add the cooked pasta and seared chicken, tossing everything until evenly coated.

Pour the mixture into a 23 x 33cm / 9 x 13" baking dish and even out the surface. Top with the remaining cheese and bake for 25 minutes, or until golden and bubbling.