Bring a large pot of water to a boil. Salt water and cook pasta to a chewy al dente, about 8 minutes.
In a nonstick skillet, brown and crumble the sausage. Drain cooked crumbles on paper towel lined plate. Return pan to heat and add extra-virgin olive oil, butter, garlic and mushrooms. Season liberally with salt and pepper. Saute 3 to 5 minutes, until mushrooms are lightly golden.
Preheat broiler to high.
To mushrooms, add flour and stir, cooking 2 minutes. Whisk in stock, then stir in cream. Bring cream to a bubble, then stir in 2 cups of 4 cheese blend. When cheese has melted into sauce, add tomatoes. When sauce comes to a bubble, remove from heat and adjust seasonings, adding hot sauce if desired.
Combine cheese sauce with sausage and pasta, transfer to flameproof baking dish, casserole or flameproof serving platter. Sprinkle remaining 1/2 cup of 4 cheese blend and the grated Parmesan over the top and brown under hot broiler.