Chop the cauliflower. Bring the vegetable broth to a boil over medium high heat and add cauliflower. Cook until cauliflower is soft, about 15 minutes. In my experience, the longer you cook it, the smoother the sauce will be. Meanwhile, melt the butter in a large skillet over medium heat. Add the minced garlic and saute for 4-5 minutes or until soft and fragrant.
As the garlic and cauliflower are cooking, bring a large pot of water to boil and cook the fettuccine according to directions on package, reserving some of the starchy water to add to the sauce later.
Transfer cauliflower to a blender with about 2 cups of the broth. You may need to do this in batches depending on the size of your blender. Add the sauteed garlic, salt, nutmeg, and black pepper and puree until very smooth, about 5 minutes. Once the mixture is moving, stream the olive oil into the blender. Add more broth or water if the mixture is too thick to move through the blender. You want it to turn through the blender easily. When puree is very smooth, transfer back to the butter/garlic skillet.
Add the cream and cook over low heat. Add the starchy pasta water (or regular water if you’re not making pasta) and keep warm until ready to serve. Combine noodles and sauce in a large pot or skillet and serve immediately.