Prepare the marinade – In a small bowl, whisk together the Finnish-style mustard, honey, olive oil, white wine vinegar, minced garlic, dill, thyme, salt, and black pepper.
Marinate the chicken – Place the chicken leg quarters in a shallow dish or a resealable bag. Coat thoroughly with the mustard mixture, ensuring even coverage. Let marinate for at least 30 minutes, or up to overnight for deeper flavor.
Preheat the oven – Set the oven to 400°F (200°C). Line a baking sheet with parchment paper.
Roast the chicken – Arrange the marinated chicken on the baking sheet and roast for 35-40 minutes, basting once with the pan juices, until golden brown and the internal temperature reaches 175°F (80°C).
Cook the potatoes – While the chicken roasts, place the halved new potatoes in a pot of salted water. Bring to a boil and simmer for 12-15 minutes until tender. Drain and toss with butter and lemon zest.
Prepare the asparagus – In the last 5 minutes of cooking time, add the asparagus to the baking sheet with the chicken, allowing it to roast until tender-crisp.
Serve – Plate the roasted chicken alongside the buttery potatoes and asparagus. Garnish with extra fresh herbs if desired.