Return the cracked shells to the stockpot, mashing them with a wooden pestle or spoon, or using a cracker to break apart the large pieces of shell. Add the carrots, onion, parsley, thyme, ginger, and celery. Cover the shells and vegetables with water—just—and set over high heat. Bring to a boil, reduce the heat to a simmer, and skim off any scum that rises to the top. Simmer for 1 hour, uncovered, stirring occasionally. Strain the stock and return the liquid to the pot. Set over medium heat and reduce for another 30 minutes, or until there’s about 2 cups of liquid. Set aside.