Preheat oven to 350°F and line baking sheets with parchment paper.

Add all ingredients to the bowl of a standing mixer. Mix until combined.

Make one inch balls of cookie dough by rolling between your hands. Place two inches apart on the baking sheets. Bake for 8-10 minutes. You'll want to see cracks along the top. Allow to cool on the baking sheet for 5 minutes and then transfer to a cooling rack to cool completely.

In a medium bowl, combine butter and sugar with a hand mixer or a stand mixer. Add the vanilla and milk, one tablespoon at a time. You may not need all four, keep adding until you have a good spreadable consistency. Mix on high for a couple minutes until fluffy.

When the cookies are cool, spread filling on one cookie and top with another cookie, making a sandwich. Enjoy!