This is an easy and delicious bar recipe with a light and flaky shortbread crust, a creamy caramel filling, and a crumb topping. The recipe is from the wonderful cookbook, "The Modern Baker," by Nick Malgieri and was chosen Top Cookie Recipe of 2008 by the Washington Post. It's Malgieri's favourite recipe in the book and it might just become yours too! Save the wrappers from the softened butter sticks to grease the parchment. Note that the flour measurement calls for it to be spooned into the cup and leveled off--this will give you a different amount of flour in the cup than the dip and sweep method and noticeably effect the texture of the crust. MAKE AHEAD: Store in an airtight container at room temperature if you are serving them within a day. Or wrap and freeze for up to 2 months, making sure to bring the bars to room temperature before serving.