In a large saute pan melt butter and add onions. Saute until cooked through and well browned. Ease crawfish into onion mixture and add salt, pepper and cayenne. Cook for 3 minutes. Add Velveeta and heavy cream. Pour over drained fettuccini. Top with Parmesan. In a preheated 350-degree oven, bake for 15 to 20 minutes. Remove and serve.
Recipe courtesy of Thomas Gosney