Preparing the Lemon Shortbread Cookies:

Preheat and Prepare:

1. Preheat your oven to 300°F (150°C). Line a baking sheet with parchment paper or a silicone baking mat to prevent the cookies from sticking.

Combine Dry Ingredients:

1. In a medium-sized bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.

Cream the Butter and Sugars:

1. In a large mixing bowl, using an electric mixer fitted with the paddle attachment, beat the unsalted butter, granulated sugar, light brown sugar, lemon zest, lemon juice, and vanilla extract on medium-high speed until the mixture is smooth and well-combined. This should take approximately 2-3 minutes.

Incorporate Dry Ingredients:

1. Gradually reduce the mixer speed to low and slowly incorporate the flour mixture. Mix until just combined, ensuring not to overmix. The dough will be slightly thick.

Shape the Cookies:

1. Using a 1-tablespoon-sized cookie scoop or spoon, form the dough into small balls. Place them on the prepared baking sheet, spacing them 1 ½ inches apart. Flatten each ball slightly with the bottom of a glass dipped in flour to prevent sticking.

Bake:

1. Bake the cookies for 15-20 minutes or until the edges are lightly golden. Note: Baking times may vary depending on your oven, but for reference, the cookies should be ready in approximately 18 minutes.

Cool:

1. Remove the baking sheet from the oven and allow the cookies to cool on the sheet for 5-10 minutes before transferring them to a wire cooling rack to cool completely.

Preparing the Lemon Glaze:

Mix Ingredients:

1. In a small bowl, whisk together the powdered sugar, fresh lemon juice, and milk until smooth and well-combined.

Apply Glaze:

1. Drizzle the glaze over the cooled cookies using a spoon, or dip the tops of the cookies into the glaze for a more uniform coating. Allow excess glaze to drip off before placing the cookies on a wire rack to set.