Chop the onions, mince the garlic cloves, peel and cube the potatoes. In a skillet saute onions, then garlic until golden brown. Add in potatoes, clam juice, pepper, salt and chicken broth. Bring to a boil. Reduce heat to a simmer until potatoes are tender - about 20 minutes. In a bowl mix together the flour and half-and-half until the mixture is smooth. Gradually stir into the soup, boil for 3 minutes or until it thickens. Stir in the clams and remaining half-and-half.