Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a stand mixer, cream together brown sugar, softened butter, and a pinch of salt on medium speed until smooth and fluffy, about 3-4 minutes.

Gradually incorporate the eggs, vanilla extract, milk, and Irish whiskey into the creamed mixture. Mix on low speed until well combined.

Slowly add the all-purpose flour and rolled oats to the wet mixture, mixing until just combined.

Chill the dough in the refrigerator for about 1 hour.

Scoop the chilled dough onto the prepared baking sheet, leaving space between each one and bake for 10-12 minutes.

Once baked, remove cookies from the oven and let them cool completely on a wire rack.

In a clean mixing bowl, beat the egg whites with brown sugar until stiff peaks form, approximately 5-7 minutes. Gently fold in the whiskey.

Pipe the meringue onto the flat side of half of the cooled cookies, topping each with another cookie to create a sandwich.