1. In a large pot, bring the broth, bay leaf, onion, celery, and carrots to a simmer. Simmer for 5 minutes. Add the sage, salt, pepper, and chicken breasts and simmer, partially covered, until just done, about 25 minutes. Turn the chicken breasts a few times during cooking.
2. Meanwhile, in a large pot of boiling, salted water, cook the cavatelli until just done, about 10 minutes. Drain.
3. In a small bowl, stir the butter and flour together to form a paste. Remove the bay leaf from the pot, push the chicken to the side and then whisk the butter mixture into the liquid. Simmer until thickened, 1 to 2 minutes. Stir in the cooked cavatelli and simmer until just heated through.
Frozen Pasta:: Several brands of frozen cavatelli, flat egg noodles, and gnocchi are available in supermarkets. Unlike dried pasta, these products have an appealing doughy chew that we find just right with this type of saucy stew. Cook the frozen pasta separately according to package directions, drain, and then stir into the pot with the chicken.
Wine Recommendation: Because this dish has no bold or assertive flavors to compete with the wine, options are unlimited: red or white, full-flavored or light-bodied. Three good choices would be a merlot or a chardonnay from California or a Meursault (also made from chardonnay) from France.