In a large pot or Dutch oven, melt the butter over medium high heat.
Add the onion and garlic and allow to cook until soft and translucent.
Add the cauliflower, stock and milk then season with nutmeg, salt and pepper.
Allow to simmer until the cauliflower is tender, approximately 10 minutes.
Transfer the sauce to a blender (or use a stick blender) and blend until smooth. You might need to add a splash more milk or stock, depending on the desired thickness.
Return the sauce to the pan and add the cheese. Allow the Parmesan to melt into the sauce.
Add cooked pasta and a splash of the pasta cooking water and toss to combine. Serve topped with more Parmesan.