In a stand mixer fitted with a paddle attachment, or in a large mixing bowl with a hand-held electric mixer, cream the butter, bacon fat, and sugar until light and fluffy, 2-4 minutes. Whisk the dry ingredients together in a separate bowl, then add to the mixing bowl and beat at low speed until barely mixed, there will still be some flour visible. Add the bacon pieces and continue mixing on low speed until just combined.
Heat oven to 375°F and line baking sheets with parchment paper.
Now it is time to form your shortbreads, and this is a forgiving dough, so feel free to get creative!
If you prefer a neat and precise edge, or fun shapes of shortbread, roll the dough between two sheets of parchment to approx. ½ inch thick and cut to your desired shape and size. Scraps can be re-rolled.
If you like larger, more traditional shortbread wedges, you can pat into rounds about ¾ of an inch thick and score with a fork into break-apart wedges.
Our preferred method is also the easiest, just roll into a log shape and chill for at least 2 hours, and then slice off round cookies. You can make these large rounds 2-3 inches in diameter or roll them small for little bite-size snack cookies about an inch wide.
Keep cookies one to one and a half inches apart on the baking sheet, they don’t spread too much. Chill on the baking sheet for 20-30 minutes minimum or up to 24 hours. This is a very important step, as you want the fat to be solid before baking, otherwise, it will melt out of your shortbread and make it dry and crumbly.
Bake for 10-18 minutes depending on the size of your cookies. They should be lightly golden brown on the edges. Cool on the pans on a wire rack for 10 minutes, then transfer from the pans directly to the rack to finish cooling. They will last up to two weeks in an airtight container, or up to three months in the freezer.