Preheat oven to 425°F.
In a small bowl, add the honey mustard sauce/marinade ingredients together and whisk well. Reserve about 3 tbsp. and then pour the rest over the chicken thighs and stir to coat.
While chicken marinates, add the potatoes and brussels sprouts to a large sheetpan. Drizzle with olive oil and and the seasonings and toss to evenly coat.
Place in the oven and cook for about 10-15 minutes to give them a head start. If your chicken thighs are on the larger/thicker side, you can do more on the 10 minutes side, and for thinner thighs, aim for the 15 minutes.
Once the veggies have roasted a bit, remove and shift them all to one side. Add the marinated chicken evenly on the sheetpan, trying keep them from touching. Discard any of the contaminated marinade.
Bake for about 20-25 minutes, or until the chicken has reached about 165°F. Shift the oven to Broil, and brush the chicken with remaining honey mustard. Broil on high for another 2-4 minutes.
Remove from oven and rest for about 5 minutes before serving. We like to drizzle some hot honey over top, especially on the veggies and sprinkle with fresh thyme.