Marinate chicken thighs in butter milk around 8 hours
Preheat oven to 350 (if you have convection roast option, use it)
Pour extra virgin olive oil in 12 inch cast iron skillet and swirl until it coats the bottom
Lift chicken thighs out of buttermilk marinade and let most of it drip off
Place chicken thighs in skillet, skin side up
Discard buttermilk marinade
In a small bowl combine dijon mustard and wine
Brush mustard mixture on top of each chicken thigh
Sprinkle chicken thighs with 1 teaspoon kosher salt, 1/2 teaspoon of black pepper, paprika and thyme
Place skillet in 350 degree oven for 30 minutes
Remove skillet from oven.
Using tongs lift chicken thighs out of skillet and put on plate.
Add the potatoes, leeks, carrots and garlic to skillet. Sprinkle with remaining kosher salt and black pepper.
Toss to coat veggies in pan juices.
Place particially cooked chicken thighs on top of veggies.
Roast chicken and veggies 30 minutes longer until chicken registers 155 degrees on instant read thermometer.
Place cooked chicken thighs on a plate and tent with foil to keep warm.
Turn oven up to 425 degrees and place skillet of veggies back in the oven for an additional 15 minutes until tender and starting to brown.
To serve, place roasted veggies on a plate and top with chicken thigh.
Sprinkle with fresh chopped parsley and additional salt/pepper if needed.