Step 1: Season the chicken - Pat the chicken thighs dry with paper towels. Season them evenly with salt, black pepper, smoked paprika, and garlic powder. Make sure both sides of the chicken are well coated with the seasoning.
Step 2: Sear the chicken - Heat the oil in a large skillet over medium heat. Place the chicken thighs skin side down and cook for several minutes until the skin becomes golden and crisp looking. You are not cooking the chicken through here. The goal is simply to develop flavor and color.
Step 3: Transfer to the slow cooker - Place the seared chicken thighs skin side up in the slow cooker. Keeping the skin facing up helps maintain some of its texture while the chicken cooks.
Step 4: Make the Carolina gold sauce - In a small bowl whisk together the yellow mustard, honey, brown sugar, apple cider vinegar, and Worcestershire sauce until the mixture is smooth and fully combined. The sauce should be thick and glossy with a bright golden color.
Step 5: Add the sauce - Pour the sauce around the chicken rather than directly over the skin. This helps keep the chicken skin from becoming too soft while it cooks.
Step 6: Slow cook - Cover the slow cooker and cook on low for 5 to 6 hours. During this time the chicken will become incredibly tender and the sauce will absorb the flavor of the chicken.
Step 7: Thicken the sauce - Remove the lid during the last 30 minutes of cooking. This allows the sauce to reduce slightly and become thicker and richer. Once done, spoon the sauce over the chicken before serving.