How to Make It
Make the garlic puree Preheat the oven to 300°. In a medium enameled cast-iron casserole, combine all of the ingredients. Cover and braise in the oven until the garlic is very tender, about 1 hour; let cool to room temperature.
Using a slotted spoon, transfer the garlic cloves to a mini food processor and puree until smooth. You will have about 1 1/2 cups of garlic puree. Strain the oil from the casserole into a 1-quart heatproof jar and discard the aromatics. Let the oil cool completely, then refrigerate; reserve for another use.
Make the clams In a medium saucepan of salted boiling water, cook the fregola until al dente, 10 to 12 minutes; drain well.
Meanwhile, in a large pot, heat the oil. Add the sliced garlic and cook over moderate heat, stirring frequently, until softened, about 2 minutes. Add the clams, wine and 1/4 cup plus 2 tablespoons of the garlic puree and stir to coat the clams. Cover and cook over moderately high heat, shaking the pot occasionally, until the clams open, 5 to 7 minutes. As they open, use a slotted spoon to transfer them to a serving bowl; discard any that do not open.
Add the fregola, lemon juice, scallions, chopped herbs and more garlic puree, if desired, to the broth; season with salt and pepper. Pour the garlic broth over the clams and garnish with chopped parsley and dill sprigs. Serve immediately with lemon wedges and crusty bread.