Preheat oven to 425 F.
Melt butter (2 tablespoons) in a large oven safe skillet.
Add yellow onions (1 chopped), salt (1 teaspoon), and pepper (1/4 teaspoon), and saute over medium heat until onions become translucent - about 7 minutes.
Lower the heat to medium-low and stir in heavy cream (1/4 cup), chicken broth (1 cup), Tabasco (1/2 teaspoon), thyme (1 teaspoon) and xanthan gum (1/2 teaspoon). Bring the combo to a gentle simmer.
Simmer sauce for about 15 minutes - you'll know it's done once the sauce has reduced by half, and it coats the back of a spoon.
Remove from heat and stir in sour cream (1 cup), until no lumps remain.
Add cauliflower rice (3 cups), chicken (2-3 cups cooked and cubed) and broccoli florets (3 cups) and toss to evenly coat.
Flatten the top of the casserole with the back of your spoon.
Sprinkle the top of your pan with cheddar (2 cups) and bread crumbs or pork rinds (1 1/2 cups).
Bake for 20 minutes, you'll know the casserole is done once it's heated through and the cheese starts to bubble. Enjoy!