Pat the chicken dry and place it breast side down. Use kitchen shears or a sharp knife to cut along both sides of the backbone, starting at the tail end and working your way up to the neck, removing the backbone completely. Flip the chicken over, press down on the breastbone to flatten it, then pull the wings and legs out to the side.
In a bowl, combine butter, sofrito, the juice of sour orange, adobo, oregano, salt, and black pepper.
Use a kitchen brush to coat the whole chicken evenly with the mixture on both sides.
Cover the chicken with foil and cook in a preheated oven at 350°F for 1 hour and 20 minutes.
Remove the foil, increase the temperature to 425°F, and cook uncovered for 40 minutes, basting halfway through. Buen provecho!