Cook bacon in a 6 quart Dutch oven or similar over medium-high heat until crisp. Remove to a paper towel lined platter to drain, then chop. Set aside.
Reserve ¼ cup drippings in pot. To the drippings add onion and celery. Cook over medium high heat for 3-5 minutes or just until tender and beginning to brown. Add minced garlic, cook for 1 minute longer.
Add flour to the pot, mixing until absorbed. Gradually whisk in chicken stock. Add diced potatoes, seafood seasoning ,salt, pepper and cayenne. Mix well.
Cover and cook for 15 minutes over medium or until the potatoes are fork tender.
Chop clams. Once potatoes are fork tender uncover and add chopped clams, reserved juice, and half and half. Bring to a gentle boil for 1-2 minutes and test thickness. (To thicken, remove some potatoes and mash then return to pot. To thin, add additional half and half.) Add half of cooked bacon back to chowder, mix until evenly distributed.
Serve immediately garnished with bacon and green onions along with garlic bread, crackers or topped with croutons.
Alternate thickening technique: Dissolve 2 tablespoons cornstarch in just enough cold half and half until dissolved. Whisk into pot, repeating until desired consistency is reached.