Heat the oven again to 425ºF. Meanwhile, finely chop 1 large shallot (about 1/2 cup) and 2 garlic cloves (about 1 1/2 teaspoons). Melt 1 tablespoon unsalted butter in a medium frying pan over medium heat. Add the shallots and cook until softened, 3 to 4 minutes. Add the garlic and cook until very tender, 1 to 2 minutes more. Scrape into a large bowl.