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

In a mixing bowl, combine softened unsalted butter and powdered sugar; cream until light and fluffy.

Add the large egg and vanilla extract, mixing until smooth and well combined.

In a separate bowl, sift together all-purpose flour and baking powder, then gradually mix into the wet ingredients.

Turn the dough onto a floured surface and shape into 1 inch thick discs; place on the prepared baking sheet.

Bake for 15-20 minutes until edges are light golden brown, centers should remain soft.

Allow cookies to rest for 5 minutes, then transfer to a wire rack to cool completely.

Melt white chocolate until smooth and fluid using a microwave or double boiler.

Spread melted white chocolate onto the flat side of one cookie and top with another cookie.

Let the assembled cookies set at room temperature for 30 minutes before enjoying.