Prep. Preheat oven to 425 F. Place defrosted green beans in a clean kitchen towel, and gently ring out water. You want to remove as much liquid from the green beans as possible, without squishing them too much.
Saute. Melt butter (2 tablespoons) in a large oven-safe skillet. Add sliced mushrooms (2 cups), yellow onions (1 chopped), salt (1 1/2 teaspoon), and pepper (1/4 teaspoon) and saute over medium heat until onions become translucent (about 10 minutes).
Simmer. Lower the heat to medium-low and stir in heavy cream (1 1/2 cups), Tabasco (1/2 teaspoon), thyme (1 teaspoon), and xanthan gum (1/4 teaspoon). Bring the combo to a gentle simmer. Cook veggies in simmering cream for 15 minutes, you'll know they're done once the sauce has reduced by half, and it coats the back of a spoon. Stir in the green beans. Taste and adjust seasoning to your liking.
Bake. Remove from heat, and sprinkle the top of your pan with cheddar and crushed pork rinds (if using). Bake for 20 minutes, you'll know the casserole is done once the beans are heated through and the cheese starts to bubble. Enjoy!
Notes
To thaw the green beans, I let them sit in the fridge overnight on a large plate.