Preheat oven to 375 degrees F. Bring a large pot of water to a boil. Grease a 9x13 inch baking dish with butter and set aside.
Boil the cauliflower florets until crisp-tender, for about 5 minutes. Drain really well and lay out on a paper towel lined plate and pat dry. Pour the cauliflower in an even layer into the prepared baking dish.
In a saucepan over medium/high heat, bring cream to a simmer. Whisk in the cream cheese and mustard until smooth. Turn heat down to low and stir in cheddar, gruyere, salt, and pepper. Stir until the cheese melts. Turn off the heat and whisk in beaten egg and xanthan gum.
Pour the sauce evenly over the cauliflower. Top with parmesan cheese and bake for 15 minutes, until the sauce is bubbling. Turn the oven to broil for 1-2 minutes to brown the top of the casserole. Garnish with fresh or dried parsley and serve warm.
You can substitute your favorite hard cheeses for the cheddar and the gruyere.1/2 c per serving
Calories: 243kcal | Total Carbs: 3g | Protein: 10g | Fat: 22g | Fiber: 1g | Net Carbs: 2g