In a medium mixing bowl - whisk together bourbon, maple syrup, mustard, jalapeno brine, brown sugar, minced garlic, oil and soy sauce.
Roughly chop half of the sliced jalapeños and add to the marinade.
Add chicken and toss to thoroughly coat.
Place chicken thighs in zip-top bag, pour marinade into the bag and seal. Marinate from 4 - 24 hrs., flipping bag over halfway through marinating time to allow all of the chicken to soak evenly.
Preheat oven to 425°F / 220°C / Gas Mark 7.
Remove chicken from marinade and pat dry with paper towels.
Place skin-side up on parchment-lined sheet pan and bake for 35 minutes, until skin is crispy and chicken reaches 165°F internal temperature.
Top with remaining jalapeno slices and serve.