In heavy pot, cook chopped bacon over medium heat until crispy. Remove with slotted spoon and set aside, leaving rendered fat in pot. Add butter to bacon fat. Sauté leeks and shallot until soft and fragrant, about 5 to 7 minutes. Add garlic and cook for another minute. Stir in diced potatoes, oyster liquor, and stock. Simmer and cook until potatoes are tender, about 10 to 12 minutes. Lower heat and stir in cream and milk. Gently add oysters and cook just until they curl and become tender, about 2 to 3 minutes. (Do not overcook—they’ll get tough.) Add thyme, salt, and pepper to taste. Ladle into bowls and top with crispy bacon and fresh herbs. Serve hot with crusty bread on the side.