Preheat oven to 375 degrees F.
Lightly steam broccoli and set aside. Just enough to where it gets bright green.
In a small saucepan, add butter and minced garlic over medium heat. After 1 minute, add cauliflower rice for 1 additional minute. Just enough to soften it slightly and infuse some garlic flavor. Set aside.
in a large bowl, add 1 cup white cheddar cheese, sour cream, mascarpone cheese, heavy whipping cream, garlic powder and garlic salt. Mix well.
Add broccoli and cauliflower and continue mixing until well coated.
Add mixture to a casserole dish.
Lightly pepper the top.
Add remaining cup of white cheddar cheese, four cheese blend and lemon pepper to the top.
Cover and bake for 20 minutes. Remove cover and bake for 5 additional minutes.