Saute garlic and butter in a pan over low/med heat until soft but not browned.
Bring water/broth to a boil in a large pot. Add cauliflower and cook for 7-10min or until it is fork tender. Do not drain.
Use a slotted spoon and transfer cauliflower to a blender. Add 1 cup of broth/water from the cauliflower pot, sautéed garlic/butter, salt, pepper, milk. Blend/puree for several minutes until the sauce is smooth. You can add more broth/water or milk depending how thin/thick you want the sauce.
Serve hot. If the sauce starts to look dry, add a few drops of olive oil , water or milk