Preheat your oven to 350 °F. Line your baking sheets with parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment or in a large bowl using an electric mixer, beat the butter and brown sugar until smooth.
Add in the icing sugar and combine until smooth.
Add in the flour slowly, with the mixer on low - this is not whipped shortbread after all- until the dough is completely mixed.
Lightly flour your work surface and turn out the dough. Roll the dough until it's a ¼ inch thick.
Cut the dough into shapes as desired. Place on the prepared baking sheets.
Pierce the top of each cookie with a fork two or three times.
Bake for 10-12 minutes, until the cookies are lightly browned.
Remove and cool on the baking sheets for several minutes, then remove and cool completely on baking racks.
Notes
Baking Tips: Make sure that there are no lumps in your brown sugar as this can lead to lumps in the cookies that don't melt.