Source: Food52
adapted by http://theresalwaysthyme.blogspot.com/
4 tablespoons softened butter
zest and juice of one lemon
1 leek, sliced, white part only
3 cloves garlic, chopped
1/2 teaspoon thyme leaves, roughly chopped (I used dried)
2 teaspoons Dijon mustard
big pinch of crushed red pepper
salt and freshly ground black pepper, to taste
1 large chicken
For the compound butter: In a food processor, combine the butter, lemon zest, juice, garlic, thyme, mustard, leek, slat and pepper.
For the chicken: Preheat the oven to 425° F.
Remove the gizzards from the chicken and discard. Rinse the chicken. Pat the chicken dry with paper towels and set it on a cutting board. Flip it onto its breast and using kitchen shears, remove the backbone by cutting carefully down each side of the bone. The entire inside of the chicken will be exposed when you’re finished. You can also pull out the breast bone, if you want to, or flip the chicken over and press down hard to crack it, the chicken will lay flatter this way.
Sprinkle the cavity with salt and pepper, and then flip the chicken over so that it lies flat. Trim any excess deposits of fat from around the cavity and tail end. Gently slide your fingers under the skin and ease it away from the meat, around both sides of the breast and both thighs and legs. Carefully smear the compound butter, underneath the skin, being careful not to tear, if you can. Reserve about a tablespoon of the butter, and then spread the reserved butter evenly over the skin, followed by a sprinkle of more salt and pepper.
Lay the chicken flat in a shallow roasting pan just large enough to accommodate it.
Roast for about 30 minutes, then baste. Decrease the heat to 375°. Put potatoes or whatever vegetables you like around the chicken to roast. Cook for another 30 minutes, basting once again in the middle, and continue to roast until the chicken is done. Let the chicken sit for a few minutes before carving; serve with the pan juices, the potatoes and some crusty bread for sopping up the juices.