In a pot over high heat, brown the mushrooms, onion and garlic in the butter. Add the meat and cook, breaking it up with a wooden spoon, until just cooked. Add the tomato paste and cook for 1 more minute, stirring constantly.
Add the broth and bring to a boil. Simmer for 30 minutes or until the liquid has reduced by half and has thickened slightly. Sprinkle with the parsley. Season with salt and pepper.
Meanwhile, in a large pot of salted boiling water, cook the spaghetti until al dente. Drain. Transfer the pasta to the meat sauce and toss to coat well. Adjust the seasoning.
With the rack in the middle position, preheat the oven’s broiler.
On a baking sheet, place 4 oven-safe bowls. Divide the pasta among the bowls and top with a slice of cheese (see note). Broil for 3 to 4 minutes or until the cheese has melted. Serve with a green salad, if desired.
If you’re not eating right away, you can refrigerate the bowls at this stage. When you’re ready, simply pop them in the oven.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.