Preheat your oven to 350°F (177°C) and line two baking sheets with parchment paper.

Drain the pumpkin in a fine-mesh strainer for about 10-15 minutes to remove excess moisture.

In a large bowl, whisk together flour, baking powder, baking soda, salt, pumpkin pie spice, cinnamon, and ginger.

In another bowl, cream the softened butter, light brown sugar, and granulated sugar until light and fluffy.

Add the egg, mixing until fully incorporated, then mix in the drained pumpkin and milk.

Gradually add the dry ingredients to the wet mixture, mixing just until no dry flour remains.

Using a cookie scoop, drop rounded tablespoons of dough on the prepared baking sheets, spaced about two inches apart.

Bake the cookies for 14-15 minutes or until the edges are firm but the centers still appear soft.

Allow them to cool on the baking sheets for a few minutes before transferring to a wire rack to cool completely.

Melt 1 cup of unsalted butter in a saucepan over medium heat until golden brown and nutty, stirring constantly.

Whip the cooled brown butter in a stand mixer until light and fluffy, gradually adding the confectioners' sugar and vanilla.

Adjust the consistency with buttermilk as needed.

Spread a generous amount of buttercream on one cookie and top it with another, pressing gently to create a sandwich.