In a large skillet, heat olive oil on medium heat and cook garlic and bay leaf until fragrant.
Add onion, carrot, and celery and sauté until golden brown.
Add the meat and break into pieces with wooden spoon.
Add red wine and let it simmer until the alcohol is evaporated (no longer strong wine smell).
Add the whole tomato and break up into small pieces with a wooden spoon. Add vegetable stock and mushrooms.
Using a fine-mesh strainer, skim off the scum and foam on the surface. This process is important to achieve a refined taste. Prepare a bowl or measuring cup filled with water to clean the sieve.
Cook the sauce, uncovered, on medium-low heat until the liquid is almost evaporated, about for 1 hour. Stir once in a while to make sure the ingredients are not stuck on the bottom of the pan. When you can draw a line on the bottom of the pan with a spatula, it's done.
Add butter and stir to combine. Season the sauce with salt and pepper to taste (make sure you taste it. Don't be shy on salt as you would eat with pasta). Serve the meat sauce on spaghetti and garnish with parsley. Grate Parmesan cheese at the table before you enjoy.
You can keep the leftovers in an airtight container and store in the refrigerator for up to 3-4 days or in the freezer for 2 months.