Drain clams through a colander into a bowl, reserving liquid and clams. Combine clam liquid and clam juice.
Cook bacon in a Dutch oven over medium-high heat until crisp. Remove bacon from pan, reserving 2 teaspoons drippings in pan. Crumble bacon; set aside. Add onion, celery, and garlic to pan; sauté 8 minutes or until tender. Add clam juice mixture, potato, and next 4 ingredients (through bay leaf); bring to a boil. Cover, reduce heat, and simmer 15 minutes or until potato is tender.
Combine milk and flour, stirring with a whisk until smooth; add to pan. Stir in clams and half-and-half. Cook 5 minutes. Discard bay leaf. Serve with bacon. Garnish with thyme sprigs, if desired.