Cook the bacon: In a skillet over medium heat, cook bacon until crisp. Transfer to paper towels. Once cool, crumble and set aside. Reserve 1 tablespoon drippings if searing chicken.
Season the chicken: Pat chicken dry. Season with salt, pepper, smoked paprika, and onion powder.
Optional sear: Heat reserved bacon drippings over medium-high heat. Sear chicken 1 to 2 minutes per side until lightly golden.
Make the glaze: Whisk brown sugar, honey, ketchup, soy sauce, vinegar, Dijon, and garlic in a bowl.
Slow cook: Place chicken in the slow cooker. Pour glaze over chicken and add butter pieces. Cover and cook on LOW for 4 to 5 hours, until chicken reaches 165°F.
Thicken the sauce: Transfer chicken to a plate. Pour cooking liquid into a saucepan and bring to a simmer. Whisk cornstarch with cold water, then whisk slurry into simmering sauce. Cook 2 to 4 minutes until glossy and thick.
Finish: Spoon thickened glaze over chicken and top with crumbled bacon. Garnish if desired. Serve with extra glaze.