Preheat the oven to 375 degrees F (190 degrees C). Lightly grease a 9x13-inch baking pan.
Spread potatoes in a single layer in the baking pan and top with onion. Stir together melted butter, honey, dry mustard, salt, black pepper in a bowl. Drizzle mixture over potatoes; toss to coat.
Roast in the preheated oven, stirring halfway through, until tender, about 35 minutes. Garnish with parsley sprigs.