Melt 3 tablespoons of the butter in a large sauté pan over medium-high heat. Add the garlic and mushrooms and cook, stirring, for 1 to 2 minutes, until the mushrooms are tender. Add the sherry and allow to simmer for 1 minute. Stir in the bread crumbs, cracker crumbs, and parsley and cook until lightly crisp, 3 to 4 minutes.