Preheat the oven to 425°F (220°C). Line a baking sheet with parchment paper for easy cleanup.
In a large bowl, toss the cubed sweet potatoes with 1 tablespoon of olive oil, a pinch of salt, and a pinch of pepper. Spread them on the baking sheet in a single layer.
Place the chicken thighs on the baking sheet alongside the potatoes. Brush the tops of the thighs with a thin layer of olive oil and season with salt, pepper, and rosemary.
Roast for about 20 minutes, then flip the potatoes and chicken. Continue roasting for another 15–20 minutes, until the chicken registers 165°F (74°C) and the potatoes are tender and caramelized.
While the chicken and potatoes roast, make the glaze. In a small saucepan, combine balsamic vinegar, honey, minced garlic, and Dijon mustard. Bring to a gentle simmer over medium heat, stirring occasionally. Let it simmer about 5–7 minutes, until slightly thickened.
When the chicken is close to finished, brush the glaze over the chicken thighs and bake for an additional 3–5 minutes to set the glaze.
Remove from the oven and let rest for a couple of minutes. Drizzle any remaining glaze over the chicken and potatoes before serving.