Melt butter and garlic in a pan over low heat. Let the garlic infuse the butter until fragrant, or when the butter completely melts and starts to bubble.
Add dry pasta, stock, milk and salt. Stir to combine, and let this come to boil.
Let pasta cook to al dente, 7-8 minutes if using pappardelle, or follow the timing on the pasta packet. Occasionally stir to evenly distribute pasta.
Add spinach, and stir to incorporate with the pasta until spinach wilts. Turn off the heat.
Immediately add parmesan, shredded cheddar, black pepper, chilli flakes and parsley. Stir until cheese melts into the sauce. Serve immediately!
