Bring a large pot of water to a boil. Salt water and cook pasta to a chewy al dente, about eight minutes.
In a nonstick skillet, brown and crumble the sausage. Drain cooked crumbles on paper towel-lined plate. Return pan to heat and add EVOO, butter, garlic and mushrooms. Season liberally with salt and pepper. Sauté 3-5 minutes, until mushrooms are lightly golden.
Pre-heat broiler to high.
To mushrooms, add flour and stir, cooking two minutes. Whisk in stock, then stir in cream. Bring cream to a bubble, then stir in two 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 baking dish, casserole or ovensafe serving platter. Sprinkle remaining 1/2 cup of 4-cheese blend and the grated parmesan over the top and brown under hot broiler.