In a pot or large skillet over high heat, brown the onion, celery and carrot in the oil. Add the wine and simmer for 5 minutes. Add the broth, tomato paste and molasses. Generously season with pepper. Bring to a boil and simmer until the sauce reduces by half, about 15 minutes. Strain through a sieve set over a pot. Add the chocolate to the pot and stir until melted. Keep warm.