Make the marinade: In a bowl, whisk together Dijon mustard, whole grain or yellow mustard, honey, olive oil, lemon juice, apple cider vinegar, garlic, smoked paprika, salt, black pepper, and red pepper flakes if using. Taste and adjust sweetness or tang as needed.

Prep the chicken: Pat the chicken thighs dry with paper towels. This helps the marinade stick and encourages better browning.

Marinate: Add chicken to a large zip-top bag or shallow dish. Pour in the marinade and toss to coat well. Marinate in the fridge for at least 30 minutes and up to 12 hours. If marinating over 2 hours, reserve a few tablespoons of the marinade beforehand for brushing later.

Preheat the grill: Heat your grill to medium-high (about 400–425°F). Clean and oil the grates to prevent sticking.

Grill the chicken: Shake off excess marinade and place thighs on the grill. Cook 5–7 minutes per side, turning once, until nicely charred and the internal temperature reaches 165°F. Total time varies by thickness, usually 10–14 minutes.

Brush and glaze: In the last 1–2 minutes, brush the thighs with the reserved marinade or a quick mix of honey and Dijon for a shiny finish. Don’t brush with marinade that touched raw chicken unless you’ve boiled it first.

Rest and serve: Transfer to a plate and rest for 5 minutes. Garnish with chopped parsley or thyme. Serve with grilled corn, a simple salad, or roasted potatoes.