Heat butter in a large skillet over high heat. Season drumsticks with salt and pepper and quickly brown in skillet. Transfer to crock cooker once browned.
In a medium bowl, whisk together remaining ingredients (Dijon through onion powder), include some more salt and pepper. Pour mixture all over drumsticks and cook on LOW for 7 to 8 hours or on HIGH for 3 to 4 hours.
Chicken should be fork tender or temp at 170-180 degrees. Remove half the chicken and set aside for lunch the next day. Serve with sauce.