Steps
1. Boil the pasta in salted water until it's al dente.
2. In a medium skillet, add the butter, onion and sausage. Cook for about 5 minutes, or until the onion is softened and the sausage is lightly browned.
3. Add the flour into the skillet and mix everything together.
4. Slowly add the whole milk to the skillet, stirring constantly.
5. Bring the sauce to a boil, reduce the heat and cook, stirring often, until the sauce has thickened. Add the salt and pepper.
6. Strain the cooked pasta and add it to the sauce. Cook for an additional 5 minutes.
7. Serve the pasta in a plate, sprinkle the cheese and enjoy!