Step 1Combine the onions, carrot, celery, bay leaves and thyme in a large saucepan. Add 6 cups cold water, then bring to a boil over high heat.
Step 2Generously salt the water, then lower in the chicken legs. They should be barely covered by the water. Return to a simmer, then cover, reduce the heat to low and poach until the meat is very tender and has pulled away from the bones, 45 to 50 minutes.
Step 3Transfer the chicken to a bowl to cool slightly; keep the stock simmering uncovered on the stove. Scrape the mole into a large, deep skillet or saucepan and set over medium heat. Bring to a simmer, stirring often to prevent the sauce from scorching. Ladle in enough of the simmering chicken stock to thin the mole to a pourable, less pasty consistency, about ½ cup.
Step 4Discard the skin and bones from the chicken and pull the meat into large chunks. Transfer to the simmering mole sauce and fold to evenly coat. Add more chicken stock if you’d like a thinner sauce. Top with cilantro, green onions, radishes and sesame seeds. Serve hot with rice and tortillas.