Preheat oven to 450 degrees F.
Bring large pot of water (I use a 5 quart dutch oven and fill it about 5 inches to the top. You're looking to give the cauliflower room to float) to boiling. Stir in all of cauliflower ingredients, then put in cauliflower, core side facing the ceiling (so top of head down). Simmer for 15 minutes, until cauliflower is fork tender.
Drain cauliflower, and carefully place it on parchment lined sheet pan. Whisk crust ingredients together and brush all over cauliflower crust (if your cauliflower is really large, use an extra tablespoon of oil when mixing the ingredients up). Bake for 40 minutes, until crust is charred and brown. You can broil for a few minutes at end to really get crispy edges.
Meanwhile, heat butter in a saucepan on medium to melt. Whisk in flour, and cook for 2 to 3 minutes, stirring constantly, so flour can get heated through. Then whisk in cream and milk, until smooth. Add salt and bring to a boil, then turn down to simmer. Cook for 10-12 minutes, until sauce starts to thicken.
Add shredded cheese and whisk, until melted. Cook for one minute, than add rosemary, parsley and a few gratings of fresh nutmeg. Taste, and add a little salt if needed.
Pour over warm cauliflower, and reserve some for dipping.