In a bowl, combine 2 tablespoons coconut flour, kosher salt, and black pepper. Toss the beef pieces in the mixture until evenly coated.
Heat 2 tablespoons of avocado oil in a large Dutch oven or heavy-bottomed saucepan over medium-high heat. Sear the coated beef for about 5 minutes, stirring occasionally, until browned on all sides. Remove with a slotted spoon and set aside.
Reduce heat to medium. Add the remaining 1 tablespoon of avocado oil. Sauté the garlic, onion, celery, and radishes for about 5 minutes until softened and fragrant.
Pour in the Worcestershire sauce and apple cider vinegar. Scrape up any browned bits from the bottom of the pan with a wooden spoon. Let the liquid cook down for 2 minutes.
Return the browned beef to the pot. Add water, Dijon mustard, dried parsley, and dried thyme. Stir well to combine. Cover with a tight-fitting lid, reduce heat to low, and simmer for 1 hour.
Remove the lid and sprinkle xanthan gum evenly over the surface. Whisk it in quickly to prevent lumps. Increase heat to medium and simmer uncovered for 15 minutes until the broth reduces into a rich gravy.
Preheat your oven to 375°F (190°C). Melt the butter in a microwave-safe bowl. Add erythritol, almond flour, coconut flour, salt, garlic powder, baking powder, and xanthan gum. Mix in the egg, fresh thyme, almond milk, and shredded cheddar until a thick, slightly sticky dough forms.
Transfer the hot stew into an oven-safe casserole dish or large cast iron skillet. Divide the biscuit dough into 8 equal portions and drop them evenly over the top of the stew.
Bake at 375°F for 25 minutes, until the biscuit tops are puffed and golden brown. Let rest for 10 minutes before serving to allow the gravy to thicken further.