Say penne pasta and French onion soup had a baby… (What? The food stork brought them a baby. The one on the cover of a pickle jar.) The result of such a union would be something like this, with melty cheese and onion-y chicken and mushrooms mixed with toothsome penne pasta. These blessed ingredients are then baked to perfection (for 6-8 minutes, not 9 months. Don't burn your house down!) The result? Delicious weekday meal that you don't have to buy a car when it turns 16.
Once water is boiling, add pasta and cook until al dente, 9-11 minutes.
Reserve ½ cup pasta cooking water. Drain pasta in a colander. Set aside.
While pasta cooks, prepare ingredients.
Prepare the Ingredients
Halve and peel onion. Slice halves into thin strips.
Cut mushrooms into ¼" slices.
Crush croutons into coarse crumbs.
Pat chicken breasts dry and, on a separate cutting board, cut into 1" pieces. Season with ¼ tsp. salt and a pinch of pepper.
Cook the Chicken and Vegetables
Place a large oven-safe non-stick pan over medium-high heat and add 1 tsp. olive oil. You may also use cast iron skillet, or transfer to a casserole dish coated with cooking spray after step 4.
Add chicken to hot pan and cook undisturbed until browned, 2-3 minutes.
Then stir occasionally until browned on two sides and reaches a minimum internal temperature of 165 degrees, 2-3 minutes.
Transfer chicken to a plate. Keep pan over medium-high heat and add 2 tsp. olive oil.
Add onions, mushrooms, garlic, ¼ tsp. salt, and a pinch of pepper to hot pan. Stir occasionally until caramelized, 6-8 minutes.
Make the Sauce
Add cream, chicken demi-glace, pasta cooking water, and chicken and any accumulated juices to pan. Stir constantly until thick enough to coat the back of a spoon, 3-5 minutes.
Remove from burner and stir in pasta.
Bake the Pasta
Top pan with crushed croutons, then mozzarella.
Bake in hot oven until cheese is melted, 6-8 minutes.
Serve family-style. Bon appétit!