Lightly grease 4 individual soup bowls or one 6-cup baking dish and set aside.
Melt 2 tablespoons butter in a large saute pan over medium high heat.
Crumble the beef and lamb and saute until it starts to turn brown.
Add the onion, minced garlic, 3/4 teaspoon salt, and 1/2 teaspoon of the pepper, and cook, stirring, for 2 minutes.
Add the sliced mushrooms and bay leaf, and cook, stirring, until their liquid is almost all absorbed, about 4 minutes.
Add the tomato paste and cook, stirring, until starting to color, about 1 to 2 minutes. Add the flour and cook, stirring, for 1 minute. Gradually add the stock and Worcestershire sauce, and bring to a boil. Reduce the heat to medium-low, cover, and simmer until thickened, about 20 to 25 minutes.
Preheat the oven to 400 degrees F.