Place the bacon pieces in a dutch oven or soup pot (you can also do this in a separate pan while the soup cooks) and bring over medium heat. Cook, stirring occasionally, until bacon pieces are crisp. Transfer the bacon to a pile of paper towels using a slotted spoon. Drain the grease from the pot and wipe it out with a paper towel.
Place the butter and oil in the pot and bring over medium heat. Add the onion and celery and cook for 5 minutes until softened. Stir in the garlic and cook for another 30-60 seconds.
Stir together the flour, salt, and pepper in a small dish and pour over the onions and celery in the pot. Stir together until the vegetables are coated and cook, stirring occasionally, for 1-2 minutes. Add the broth, bottle of clam juice, and reserved juice that was drained from the canned clams along with the thyme and bay leaf. Whisk together, scraping up any bits off the bottom of the pot, for 1-2 minutes.
Add the potatoes and increase the heat to high to bring to a boil. Once boiling, stir and then cover and reduce heat to low to simmer. Simmer covered for 15 minutes until potatoes are tender. Remove bay leaf.
Stir in the half and half and the chopped clams and simmer uncovered, stirring occasionally, for 3-4 minutes until warmed through. Makes 9 (1 cup) servings. Top each serving with a sprinkle of parsley and 2 teaspoons of crumbled bacon