For the brine, bring 2 qts. water to a boil. Add salt and stir until dissolved. Remove from heat and add bay leaves, garlic, peppercorns and herbs. Let cool completely.
Rinse chicken(s), making sure to remove the giblets and remove excess fat. Put the chicken in a pot or container large enough for the birds and brine. Pour the brine over the chickens and add enough water to cover them completely. Refrigerate and let sit for 24-48 hours. Rotate the chickens once during that period.
Preheat oven to 425 degrees. Remove the chicken from the brine and pat dry. Remove the herbs and garlic from the brine and stuff into the cavity. Brush outside with butter or olive oil. Put onions in the bottom of a roasting pan and place the chickens on top.
Roast the chicken for 1 1/2 hours, or until the juices run clear when you cut between a leg and thigh. For a nice crispy skin, baste the chicken with butter every 15 min. After 45 min., lower the oven to 350 degrees and baste chickens in their own juices every 10-15 min. until done. Pull from the oven and let the chicken rest covered for 15 min.