Boil a large pot of water, salt and add penne. Cook until al dente. Drain and set aside.
Heat a large pan and melt butter, add garlic and onion until lightly brown.
Add diced chicken, stir to combine and allow to brown.
In a small bowl, make a cornflour/cornstarch mix by adding a tablespoon of milk and creating a thick paste. Add this to the chicken in the pan, then add cream and any remaining milk.
Stir continuously until the sauce has thickened. You can add more milk here if the sauce is too thick.
Add parmesan cheese, season with salt and pepper and allow chicken to cook fully.
Stir in the cooked pasta and gently combine and coat the penne with the sauce.
Top with parsley, chives and/or chili flakes (as shown in picture bottom left)