Cut down each side of the backbone of the chicken using poultry shears or kitchen scissors and remove. Flip chicken over and press down on breast bone to crack it.
Combine in a bowl the apples with lemon zest and juice, nutmeg, brown sugar, salt and pepper.
Set the chicken on a wire rack and set aside. Place potatoes and onions, and combine them with olive oil, salt, and pepper. Add apples and toss to combine.
Pat chicken dry with a paper towel and place about a tablespoon of the maple mustard butter under the skin of each breast. Rub the remainder of the butter evenly over the bird.
Set the coated chicken directly on top (or on a wire rack) of the apples, potatoes and onions and roast 45 minutes to 1 hour, or until it reaches an internal temperature of 165°F.