In a blender, combine the ice cream and the bourbon. Blend on high speed until the desired consistency is reached (the longer you blend, the thicker the milkshake). In a medium glass, drizzle the caramel in a spiral around the inside of the glass. To help distribute the caramel evenly turn the glass as you drizzle. Pour the milkshake into the glass, and stop when almost full. Top with the dollop of whipped cream and a sprinkle of toffee pieces.