Preheat oven to 500 degrees.
Wash chicken carefully and pat dry. Place breast side down on a work surface.
To remove the back bone start at the thigh and cut along one side of the back bone with a kitchen shears. Turn the chicken around and cut down the other side. Place the back bone on a roasting pan or save it to make stock.
Flip the chicken over so the cut sides are down. Press firmly on the breast bone to flatten the chicken into a butterfly.
Working at the neck end, carefully slide your fingers between the skin and the breast meat on both sides of the chicken. Move them from side to side gently to open up a pocket.
Slide half the lemon slices and half the thyme between the meat and the skin on one side of the breast and half into the other side.
Sprinkle coarse salt and plenty of fresh ground pepper unto the bird.
Roast in the preheated oven for 30-45 minutes. The smaller the bird, the faster the roasting time. Use a digital thermometer to make sure the chicken reaches 160 at the thickest part of the breast.
Remove the chicken from the oven and allow it to rest for 5-10 minutes after coming to temperature. This allows the juices to settle into the meat so that they will stay in the meat when you carve the bird. Enjoy!