Place the chicken in a medium pot cover with 4 cups of cold water, add a bay leaf, and 2 teaspoons of salt. Bring to a simmer and cook for 15 more minutes.
Remove the pot from the stove, discard the bay leaf and drain the liquid, reserving about 1 1/2 cups of it; you're going to need it for the sauce. Slice the chicken into 3/4 inch thick strips and return to the pot.
Melt the butter in a frying pan over medium heat. Add the onion and cook until soft and translucent, not brown, for about 6 to 7 minutes. Add the spices and cook stirring for 1 more minute, then remove from the heat.
In a food processor, combine the walnuts, garlic, and spiced onion, pulse until finely ground. Keep the food processor running and start slowly adding the reserved chicken broth until your sauce is smooth and velvety.
Pour the walnut sauce over the chicken and return the pot to the stove. Bring to a simmer over low heat. Adjust the seasoning to taste and simmer for a couple more minutes, or until the chicken is heated through. Then remove from the heat and let the chicken cool to room temperature. Serve cold or slightly warm drizzled with a finishing oil of your choice.