Preheat your oven to 425°F (220°C) and line a large baking sheet with parchment paper or a silicone mat for easy cleanup.
In a small bowl, whisk together the honey, Dijon mustard, whole-grain mustard (if using), minced garlic, smoked paprika, salt, pepper, lemon juice, and thyme. This will be your glossy glaze and flavor base.
Toss the potato chunks in about 1 tablespoon of olive oil and a pinch of salt. Spread them in a single layer on the baking sheet. Nestle the chicken thighs among the potatoes, skin-side up if you have skin, or just evenly if they’re skinless.
Pour half of the honey-mustard glaze over the potatoes and chicken, turning items so every piece gets a light coat. Reserve the remaining glaze for brushing during cooking.
Roast for 15 minutes, then give everything a gentle stir, re-coat with the remaining glaze, and return to the oven for another 15-20 minutes, or until the chicken reaches an internal temperature of 165°F (74°C) and the potatoes are tender and caramelized along the edges.
If you’d like extra crispiness on the potatoes, switch the oven to broil for 2-3 minutes at the end, watching closely so nothing burns. Remove from the oven and let rest for 5 minutes before serving.