Preheat the oven to 500°F by setting the oven rack in the upper-middle. Use sharp kitchen shears to remove the spine from the chicken. Cut into five to six pieces of approximately 1-inch length. Set spine aside. Flatten the chicken by placing it skin-side up on a cutting board. Apply firm pressure to the breastbone. Transfer chicken to a wire rack and place on a foil-lined baking sheet. Place chicken in a position so that the breasts align with the center of the baking sheet, and that the legs are near to its edge.
Use 1 tablespoon of olive oil to drizzle chicken. In a small bowl, combine 1 tablespoon of kosher salt, 1/2 teaspoon ground pepper, and 1 teaspoon baking soda (if desired). Sprinkle the mixture all over the chicken. Sprinkle mixed herbs on chicken. To evenly distribute the season, rub the chicken.
Place a wire rack on a rimmed baking sheet covered with aluminum foil. Bake the chicken until the thickest part close to the bone registers 150° on an instant-read thermometer. Then, roast for 45 minutes. If the chicken becomes too dark, reduce the heat to 450°F.
After this, Heat the remaining tablespoon of oil in a small saucepan on high heat until it shimmers. Stir in the chicken spine. Cook for 3 minutes, stirring occasionally. Stir in celery, carrot, onion, and celery. Now Cook, stirring often until the vegetables begin to brown. Add bay leaf. Deglaze with vermouth, sherry, or 1 cup of water. After this, Use a wooden spoon to scrape any browned bits from the bottom of the pan. Cook for 20 minutes at a simmer. Strain solids from the pan and return the liquid to it. Boil on medium heat for about 7 minutes, until only 1/3 of the liquid remains. Mix in the soy sauce, butter, lemon juice, and heat off. Salt and pepper to taste.
After this, Take the chicken out of the oven and transfer it to a cutting board. Now cover loosely with foil and let rest for five minutes before carving. Hot jus is a good accompaniment.