Bring large pot of water to a boil, add pasta and salt and cook according to package directions for al dente.
In a large skillet, cook sausage on medium-high heat (removed from casings) until browned, breaking up with a wooden spoon. Remove to a plate. Add garlic to skillet and cook until fragrant, about 30 seconds. Be careful not to burn!
In a large measuring cup or bowl, whisk together the milk and flour until smooth and lumps are dissolved. Stir into skillet with peas, and salt and pepper. Bring sauce to a boil, and turn down to low and simmer until thickened, about 3-5 minutes. Stir the sausage back in, along with the red peppers and scallions.
After reserving a cup of the pasta water, drain the pasta and add into the sausage sauce; add cheese and toss until cheese is melted. Add in some of the reserved pasta water to loosen the sauce if needed. Season with salt and pepper to taste. Sprinkle with additional shredded parm if desired. Serve in bowls or transfer to one large serving bowl.
Optional items include swapping sweet sausage for hot sausage, or even using pork sausage, but I prefer the spicy turkey sausage. Original recipe calls for 8 oz. mushrooms. You could also use pre-grated parm, but the fresh grated (imported) is the best and gives it a great flavor! Don't skimp on the cheese!
We often have leftovers, make sure to add liquid (milk or water) when re-heating; pasta will absorb liquid as it sits.