1. Preheat the oven to 300°F (150°C) and line the cups of mini-muffin pans with paper liners (petits fours size)
  2. Using electric beaters or a stand mixer fitted with the paddle attachment, beat the butter and icing sugar on medium speed until smooth and light. Beat in 2 of the egg yolks. Add the flour, cornstarch, and 1 tsp (5g) salt and mix on low speed until the dough comes together.
  3. Use a small ice cream scoop or 2 teaspoons to drop the dough into the lined muffin pans. Use the bottom of a glass dipped in flour to gently press the dough flat. Whisk the remaining egg yolk with 1 Tbsp (15 mL) of cold water and brush the tops of the cookies. If you wish, sprinkle the cookies with a little flaked sea salt.
  4. Bake for 35 to 45 minutes, until the tops are a rich golden brown. Let cool in the pans on a wire rack.

Make Ahead
You can store baked shortbread in an airtight container at room temperature for up to 3 weeks. It also freezes wonderfully well because of its low sugar content (relative to other holiday cookies). You can make the dough ahead and freeze it in a resealable bag for up to 3 months. Thaw the dough for 2 hours at room temperature before spooning it in to pans and baking. Or freeze baked shortbread in an airtight container for up to 3 months and thaw at room temperature.

Shortbread improves in texture as it sits in the pan. The longer these cookies sit, the softer and more tender they get. However, keep them away from cookies with prominent flavours (such as chocolate, spices, or citrus zest) as they will absorb the odours and flavours around them.

Recipe from Set for the Holidays with Anna Olson, Appetite by Random House, 2018