In a small bowl, combine the brown sugar, mustard, maple syrup and rice vinegar.

Whisk until completely smooth and well incorporated.

In a baking dish, lay the chicken thighs in and sprinkle evenly with sea salt and fresh black pepper.

Turn the thighs over and repeat on the remaining side.

Pour about 2/3 of the sauce over the chicken, tossing to coat well, and set aside the remaining sauce for grilling.

Cover the chicken dish with saran wrap and refrigerate for at least 30min.

Remove the meat from the fridge and let rest on the counter for 5-8 minutes. (It is always best to cook meat that is not straight out of the fridge.)

Heat your grill to medium high heat and place the thighs on the grill.

Grill for 4-6 minutes per side (depending on the size of the thigh)

Flip the chicken and baste with the sauce.

Continue to cook through, 3-5 minutes.

Remove from the grill and tent with foil.

Let rest for 2-3 minutes and then serve!