Preheat oven to 425°. Place potatoes, carrots, onion and apple on a large rimmed sheet pan. Toss with 2 Tbsp olive oil, ½ tsp salt and pepper. Nestle chicken thighs in vegetables, and sprinkle chicken with remaining 1 tsp salt. Drizzle with remaining 2 Tbsp olive oil.
Roast 25 minutes, until vegetables are easily pierced with a fork.
Whisk herbs into melted butter, and drizzle over chicken and vegetables.