Preheat oven to 350 degrees Fahrenheit. In a 6 quart pot, heat 12 cups of water and 1- 2 Tablespoons of salt on high until boiling. Add penne pasta and cook about 10 minutes or until it's al dente (slightly firm)
While your pasta is cooking, roughly chop the mushrooms, slice the yellow pepper into thin strips and dice your onion.
When the pasta is done, drain the pasta in a colander and pour the pasta into a 9x13 casserole dish. Set aside until cheese sauce is finished.
In a large saute pan, heat the butter on medium until melted. Add in mushrooms, peppers, onions, salt, pepper and old bay seasoning. Saute about 3 minutes.
Add flour to saute pan and stir to incorporate flour with the butter and vegetable mixture
Add shrimp stock and 1/2 and 1/2, stirring constantly over medium heat until sauce begins to thicken
Add in grated cheeses (except Parmesan) and cream cheese, continue to cook until cheese has melted and your sauce has thickened.
Add in tomatoes and crab meat ,stir to combine and turn heat off
Pour cheese & crab meat mixture over pasta and stir gently to combine.
Bake uncovered for 30 minutes or until you have a thick and creamy sauce.
Remove from oven, Sprinkle grated Parmesan cheese on top.
Serve and Enjoy!