Turn oven to 425ºF.
Begin Chorizo Gratin
Heat 1 tbsp. (2 tbsp. for 4 servings) of oil in a large oven-safe skillet over medium. Add onion, celery, and carrots, and saute for 5 minutes, stirring occasionally.
Meanwhile, wash and chop thyme leaves. Roughly chop spinach. Drain and rinse butter beans using a fine mesh sieve.
Add chorizo to the skillet and cook for 3-5 minutes, breaking it up with a wooden spoon. Add garlic, thyme, and flour, and stir for 1 minute. Add butter beans and sherry cooking wine. Use a wooden spoon to scrape off any brown bits stuck to the bottom of the skillet. Add 1 1/2 cups (3 cups for 4 servings) water, crumble in chicken stock cube, and stir. Reduce heat to low and season to taste with salt and pepper.
Prepare Crumb Topping
Melt 2 tbsp. (4 tbsp. for 4 servings) butter in a second large skillet over medium heat. Once melted, turn off heat and add breadcrumbs, almond flour, parmesan, and black pepper to taste.
Finish + Bake
Stir chopped spinach into skillet with chorizo until wilted. Sprinkle prepared crumb topping evenly over the chorizo and bean mixture. Place skillet into the oven and bake for 5-8 minutes, or until the crumb is evenly golden.
Serve into large bowls and enjoy!