In a large skillet over medium-low heat, melt the butter. Add minced shallot and garlic and cook 2–3 minutes until soft, translucent, and fragrant (do not brown).
Sprinkle in flour and stir constantly for 1–2 minutes until it forms a smooth paste and smells slightly nutty.
Slowly whisk in heavy cream, stirring constantly to keep the sauce smooth. Bring to a gentle simmer and cook 3–5 minutes until slightly thickened and able to coat the back of a spoon. Add salt and black pepper.
Reduce the heat to low, or remove the pan from heat. Add the parmesan gradually, whisking until fully melted and smooth before adding more.
Add reserved pasta water a little at a time (starting with ¼ cup), stirring until sauce becomes glossy and silky. Add more as needed to reach your desired consistency.
Season with a little more salt and cracked black pepper as needed. Toss immediately with hot pasta and serve right away.