Pat chicken thighs dry and season both sides with salt, pepper, and smoked paprika. Place sliced onion and minced garlic in the bottom of the slow cooker and nestle chicken on top, skin-side up.
Whisk together chicken broth, soy sauce, brown sugar, apple cider vinegar, and Dijon mustard. Pour over the chicken to coat.
Cover and cook on LOW for 4–5 hours or HIGH for 2.5–3 hours, until internal temperature reaches 165°F and thighs are tender.
Remove chicken. Stir a cornstarch slurry into the cooking liquid and simmer on HIGH for 5–10 minutes until thickened, then spoon over chicken.
Serve over rice, mashed potatoes, or with crusty bread. Garnish with chopped parsley or green onions.
Notes
To crisp the skin, broil cooked thighs for 3–4 minutes on a foil-lined sheet.
Boneless thighs cook faster—check early to avoid overcooking.
Leftovers keep in the fridge for up to 4 days; freeze for up to 3 months.