Preheat oven to 375 and grease a 9x9 glass baking dish
Bring large pot of water to a boil. Add cauliflower and 1/2 tsp salt and cook until cauliflower is just fork tender. Do not over cook.
Drain cauliflower well and place back in pot. Set aside.
In a small sauce pan, bring cream to a simmer, stirring well to avoid scorching.
Whisk in cream cheese and mustard and stir until mixture thickens.
Remove from heat and whisk in 1 cup shredded cheese and seasonings.
Pour over cauliflower and gently mix to combine.
Place cauliflower in prepared dish. Sprinkle with remaining cheese and bake until cheese is bubbly and slightly browned, or about 15 minutes.
For an extra bubbly topping, broil on high for 2-3 minutes but be sure to watch carefully