1 cup milk chocolate chips or semi-sweet chocolate chips
Line 13 x 9 x 2-inch pan with foil. Melt ¾ cup (1½ sticks) butter; combine with graham cracker crumbs. Press crumb mixture evenly in bottom of prepared pan.
Combine sugar, evaporated milk, remaining ¼ cup (½ stick) butter and marshmallows in large saucepan. Heat over medium heat, stirring frequently, until mixture comes to a boil. Boil 5 minutes, stirring constantly. Remove from heat. Add 2 cups semi-sweet chocolate chips, stirring until chips are melted.
Immediately pour over crust, spreading evenly. Sprinkle surface with milk chocolate toffee bits and milk chocolate chips, pressing in lightly. Refrigerate until firm, about 2 hours. Cut into bars. Store leftover bars covered in refrigerator.