Preheat your oven to 400°F (205°C).

In a large mixing bowl, combine chopped carrots, parsnips, Yukon Gold potatoes, and red onion. Drizzle with olive oil, rosemary, salt, and pepper, toss until evenly coated, and spread in a single layer in a baking dish.

In another bowl, whisk together Dijon mustard, heavy cream, olive oil, honey, garlic powder, onion powder, dried thyme, paprika, salt, and pepper until smooth and well-combined.

Pat chicken thighs dry. Arrange the thighs on top of the prepared vegetables in the baking dish. Brush the Dijon cream sauce over each chicken piece.

Place the dish in the oven and bake for 40-45 minutes until the chicken is golden brown and reaches an internal temperature of 165°F (74°C).

Optional: Switch to broil for the last 2-3 minutes for a crispy, golden crust.

Let the chicken rest for about 5 minutes before serving alongside the roasted root vegetables, drizzled with remaining sauce.