Preheat your oven to 400°F (200°C). Line an extra-large 18x13-inch rimmed baking sheet pan with parchment paper or heavy-duty foil for easy cleanup.

In a small bowl, whisk together the aged balsamic vinegar, honey, Dijon mustard, 1 tablespoon olive oil, minced rosemary, fresh thyme, and red pepper flakes until glossy and emulsified.

Place the diced sweet potatoes, halved Brussels sprouts, and red onion wedges onto the sheet pan. Drizzle with 2 tablespoons olive oil, season with ½ teaspoon salt and ¼ teaspoon pepper, and toss with your hands until every piece is glistening. Spread the veggies across the pan, leaving space in the center.

Nestle the chicken thighs into the center of the sheet pan among the vegetables. Season the chicken with the remaining ½ teaspoon salt and ¼ teaspoon black pepper. Generously brush half of the honey balsamic glaze over both sides of each chicken thigh.

Slide the sheet pan into the center oven rack and roast at 400°F (200°C) for 20 minutes.

Carefully remove the sheet pan from the oven. Brush the remaining honey balsamic glaze generously over the chicken thighs, and use a spatula to toss and flip the vegetables so they caramelize evenly in the flavorful pan juices.

Return the pan to the oven and roast for an additional 10 to 12 minutes, until the chicken reaches an internal temperature of 165°F (74°C) with sticky, mahogany caramelized edges and the sweet potatoes are fork-tender.

Remove from the oven, garnish with chopped fresh parsley, and let rest for 5 minutes. Spoon warm pan juices over the chicken and vegetables right before serving!