2 tablespoons extra-virgin olive oil
1 large celery rib, finely chopped
1 carrot, finely chopped
1 small onion, finely chopped
3 ancho chiles—stemmed, seeded and cut into small pieces
2 cups chicken stock or low-sodium broth
1 cup ketchup
1/4 cup distilled white vinegar
1/4 cup molasses
1/4 cup dark brown sugar
1/4 teaspoon dry mustard
Salt
Rack of 6 ribs, at room temperature