Make the mashed potatoes: Place chopped potatoes in a pot, cover with salted water, and bring to a boil. Cook until tender, about 15 minutes. Drain and mash with milk, butter, salt, and pepper until smooth. Keep warm.

Prepare the meatballs: In a bowl, combine ground chicken, breadcrumbs, chopped onion, beaten egg, garlic, Dijon mustard, salt, and pepper. Mix gently until just combined.

Shape mixture into 16–18 small meatballs (about 1½″ diameter).

Heat olive oil in a large skillet over medium heat. Add meatballs and cook, turning occasionally, until browned on all sides and cooked through, about 10–12 minutes. Remove meatballs to a plate.

Make the sauce: In the same skillet, lower heat to medium-low. Stir in Dijon mustard, honey, whole‑grain mustard, and chicken broth. Cook, stirring, until smooth and warmed through, about 2–3 minutes. Season with salt and pepper.

Return meatballs to the skillet, tossing to coat evenly in the honey mustard sauce. Cook for another minute so the flavors meld.

Serve: Spoon mashed potatoes onto plates, top with meatballs and extra sauce from the pan. Garnish with fresh parsley if desired.