Melt the ghee or coconut oil in a large skillet over medium-high heat; add chicken and cook until browned on the outside; transfer to a large slow cooker and top with leek, garlic, and mushrooms.
In a small bowl, combine the next 8 ingredients (mustard through wine); pour mixture over chicken, leek, garlic, and mushrooms. Cover and cook on LOW for 8 to 10 hours.
Remove chicken from slow cooker and transfer juices to a large skillet; cook over medium-high heat for 4 minutes or until slightly reduced. Whisk in coconut flour than lower heat and simmer for 10 minutes; serve over chicken.