Clam Chowder with Root Vegetables and Thyme

Name: Clam Chowder with Root Vegetables and Thyme
Ingredients: 1 tablespoon olive oil; 2 slices thick-cut bacon, cut into 1/2-inch pieces; 1 medium yellow onion, chopped; 1 large leek, white part only, thinly sliced; 1/2 small celery root, peeled, cut into 1/2-inch dice; 1/2 pound small fingerling potatoes, cut into 1/4-inch thick coins; 1 1/2 cups whole milk, or more as needed; 1 cup heavy cream; 1/2 cup chicken stock; 3 sprigs fresh thyme, plus extra for garnish; 1 bay leaf; 24 littleneck clams; Salt and freshly ground black pepper