Preheat oven to 400 degrees. Using sharp shears or a kitchen knife, remove the spine from the chicken and set aside. Flatten the chicken by applying pressure to the breast bone and if desired, pop out the keel bone. Season chicken with salt and pepper and place on a wire rack set over a rimmed baking sheet.
Roast for 35-45 minutes or until the internal temperature of the breast reaches 150 degrees and thighs register 170 degrees.
Meanwhile, heat olive oil in a small pot over high heat and cut the chicken spine into 1 inch pieces. Brown these pieces well, then add soy sauce, ginger, garlic, green onion, and 1 cup water. Simmer this mixture until it is reduced by half. Strain the mixture or lift out the bones, garlic, scallion, and ginger with a slotted spoon. Season with salt and pepper and swirl in the butter while still warm. Serve the au jus with the roasted chicken and a side dish of your choice, such as rice or roasted carrots and potatoes.