Preheat oven to 375 degrees.
Bring a large pot of water to boil and season with salt.
Cook cauliflower in boiling water until tender crisp and drain well.
I usually cook my cauliflower well ahead of time so the water has time to drain.
Spray or butter an 8 x 8 ceramic or glass dish and set aside.
Bring cream to a simmer in a saucepan and whisk in cream cheese and Dijon mustard until mixed well.
Stir in one cup of Cheddar cheese and Gruyere, pepper, garlic and onion powder.
Whisk until cheese melts and it is smooth.
Remove from heat and pour over cauliflower and combine well.
Top with remaining cheddar cheese and bake about 20 minutes or until browned and bubbly