Preheat oven to 450�F and line a baking sheet with foil. Tear bread into pieces and in a food processor pulse until finely ground.
In a large bowl stir together 2 cups bread - crumbs, Parmesan, sage, salt and pepper to taste. Melt butter, add salt and pepper to taste.
Pat chicken dry and brush all over with mustard mixture. Roll chicken in bread-crumb mixture, pressing gently to adhere, and arrange chicken, without crowding, on baking sheet.
Drizzle with butter and bake in the middle of oven until cooked through and golden, 25 to 30 minutes.