Melt fat over medium heat, and cook the sausage until browned. Using a slotted spoon, remove the sausage from the pan and set aside. Drain fat if necessary, leaving 2 T. fat in the pan.
Add the scallions and garlic and cook for a minute. Stir in the flour and cook, still stirring, for a couple of minutes more. Stir in the tomatoes with their juice, the dried basil, pepper flakes, and salt and pepper. Also add the sausage back to the pan. Bring to a simmer, then turn the heat to low and cook for 30 minutes while you boil and drain the noodles.
Stir in the heavy cream, heat through. Taste for seasoning, adjusting if necessary. Serve over hot noodles. Garnish with fresh parsley or basil or both.