1/4Cpork rind breadcrumbsprocess plain pork rinds in the food processor until they resemble fine breadcrumbs
1/4Cgrated parmesan cheese
Preheat oven to 350º F. Grease a 9" square gratin dish with butter.
Bring a large pot of water to a boil, salt with 2 tsp. sea salt and baking soda (will keep the beans bright green) add haricot vert. Boil for 3 minutes. Meanwhile, prepare an ice bath in a large bowl. After beans have boiled for 3 minutes, transfer to the ice bath to stop the cooking. Drain on a kitchen towel. and set aside.
Heat a large 12" heavy skillet (I use cast iron) over medium heat and add bacon. Cook until crisp, about 10 to 12 minutes. Remove. Crumble when cooled.
Add onions to hot pan & cook in the bacon drippings stirring occasionally until they begin to soften 2 to 3 minutes. Add mushrooms & 1/2 tsp sea salt and cook, stirring, until the mushrooms begin to release their juice and they are tender about 8 minutes.
Add crème fraîche, cream, & Gruyère, thyme, & black pepper. Stir until combined and melted. Add green beans, and bacon. Mix with a big spoon until everything is mixed together. Taste for seasonings and adjust to your preference. Transfer green bean mixture to the baking dish.
Sprinkle keto breadcrumbs evenly over the top of casserole.
Bake casserole uncovered for 20 minutes, or until the keto breadcrumbs are golden brown and the tips of the beans are just starting to brown and it is warmed through.