Chicken: Cook in a single layer without crowding the pan. If the chicken is crowded, it will steam instead of developing that golden-brown crust.
Garlic: Don't reduce the count if you're nervous about 8 cloves. Cooked gently in the butter, it mellows completely without that raw bite by the time the sauce comes together.
Parmesan: Grate it yourself from a block. Pre-shredded cheese is coated in starches that prevent smooth melting and can leave the sauce grainy instead of silky.
Adding the milk and cream: Pour it into the butter-flour mixture slowly, whisking constantly. This prevents lumps and gives you a smooth, even sauce.
Lemon zest: Stir it in at the very end, off the heat, right after the parmesan melts in. Adding it too early cooks off the bright citrus oils and you lose the lift it's meant to give the sauce.
Reserved pasta water: Don't skip this step. The starch helps loosen the sauce to the right consistency and helps it cling to the noodles instead of pooling at the bottom of the bowl.
Storage: Refrigerate in an airtight container for 3 to 4 days. This recipe does not freeze well, the sauce will separate into oil and liquid once thawed, so it's best enjoyed fresh.
Reheating: Place the pasta in a skillet over low heat. Add a splash of milk, cream, or water, about 1 to 2 tablespoons, and toss gently until warmed through. This replaces the moisture the sauce loses in the fridge without breaking it.
