Place the chicken in a pan and cover with water. Add the bay leaf, onion, and salt and pepper. Bring to a boil, then reduce the heat and simmer for 20 to 30 minutes, or until tender but firm.
Remove the chicken pieces from the pan with a slotted spoon, pass the stock through a fine sieve, and skim off and discard as much fat as possible. Measure the stock; you should have about 3 cups. If it is more, reduce it over high heat. If it is less, add a little water.
Heat some olive oil in a deep skillet. Lightly dredge the chicken with flour and fry until golden brown on all sides. Transfer the fried pieces to paper towels and keep warm.
Discard the frying oil from the skillet and wipe with paper towels. Heat 3 tablespoons of olive oil over low heat, and whisk in the 3 tablespoons of flour. Continue whisking for about 1 minute, until it begins to froth.
Remove from the heat and add the garlic, reserved stock, wine, vinegar, and walnuts, whisking constantly. Return to the stove and continue whisking over medium heat until the sauce begins to thicken. Taste and add more salt and pepper if necessary.
Arrange the chicken on a heated plate, and pour the sauce over it. Sprinkle with almonds and serve immediately.