How to Make It
Stir together paprika, 1 1/2 teaspoons salt, dry mustard, thyme, and garlic powder in a small bowl.
Sprinkle spice mixture evenly over both sides of chicken thighs. Heat a large cast-iron skillet over medium-high. Add 1 tablespoon oil; swirl to coat. Add 4 chicken thighs to skillet. Cook, undisturbed, until spice mixture darkens, 4 to 6 minutes per side. Transfer to a 6-quart slow cooker. Wipe skillet clean, and repeat procedure with remaining 1 tablespoon oil and remaining 4 chicken thighs.
Melt butter in a small saucepan over medium until sizzling. Add onion and garlic; cook, stirring occasionally, until onion has softened and garlic is just beginning to brown, 6 to 8 minutes. Remove from heat, and stir in cider, tomato paste, Worcestershire, chili powder, Dijon, black pepper, cayenne pepper, and remaining 1 teaspoon salt until blended. Pour sauce over chicken. Turn chicken thighs with tongs to coat with sauce. Cover and cook on HIGH until chicken is tender, about 2 hours and 30 minutes (or on LOW 4 to 5 hours). Using two forks, shred chicken.
Just before serving, bring honey to a boil in a small saucepan over medium. Reduce heat to low, and cook, stirring occasionally, until honey is dark amber in color and smells like molasses, about 5 minutes. Pour into slow cooker. Stir in lemon juice and vinegar.