Cook your carrots first to soften.
While the carrots are cooking, put on pot for boiling your pasta.
Brown your chopped onion and celery in the olive oil until golden brown.
Peel the casing off your sausage and cut into small pieces. Add this to your pot with the vegetables.
Next, add the can of crushed tomatoes and seasonings and heat through with the sausage pieces and vegetables.
In the meantime, mix the flour with the milk until well combined before adding to the cooked vegetables, sausage and tomato mixture.
Cook slightly to help thicken it along before stirring in your drained pasta and placing in a large pot or casserole that you cover with a lid or aluminum foil.
Top the casserole with one cup of mozzarella cheese before covering and placing in a 375-degree oven for 20-25 minutes, depending on how your oven is regulated.