Brine the chicken, if desired, using the Simple Chicken Brine in the recipe notes. Thoroughly rinse and dry the chicken.
Let the chicken rest at room temperature for 30-60 minutes.
Spatchcock the chicken by cutting a 1 inch strip along either side of the backbone to remove it. Make a cut to the back of the breast bone. Press to help it lay flat.
Next, make four 1/2 inch deep cuts. Make the cuts between each leg and thigh joint and then into the breast just below where the wing attaches (think armpit). This promotes even and quick roasting.
Preheat oven to 400 degrees.
Prepare the sage butter by combining the room temperature butter, sage, garlic, salt, and pepper together in a small bowl.
After patting the chicken dry again, if necessary, smear the sage butter mixture on both sides (front and back) of the chicken.
Preheat a large dutch oven or other oven proof pan to a medium-high temperature.
Add the oil and then place the chicken, interior side down, into the hot pan. (The skin side of the chicken is facing up. See photo.) Make sure the chicken is laying flat in the pan.
Cook, without disturbing the chicken, for 4-5 minutes. Do not flip the chicken.
Place the dutch oven with the chicken directly into the oven and bake for 40-60 minutes. Cook time will vary depending on if the bird has been brined, the size of the bird, and if other items are being cooked in the oven at the same time.
Remove from oven when a thermometer inserted into the thigh and breast reads 160 degrees.
Let the chicken rest 10-15 minutes. Carve as desired. Garnish with the Sage Browned Butter sauce in the bottom of the pan and fresh sage leaves.