Prepare the Cookie Dough:

• In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.
• Mix in the egg, pistachio paste, and vanilla extract until well combined.
• In another bowl, whisk together the flour, baking powder, and salt. Gradually blend the dry ingredients into the wet mixture until a smooth dough forms.
• Shape the dough into a log, wrap it in plastic, and chill for at least 1 hour to firm up.

Form and Bake the Cookies:

• Preheat your oven to 350°F (175°C).
• Slice the chilled dough into rounds about ¼-inch thick and place them on a parchment-lined baking sheet, spacing them about 2 inches apart.
• Bake for 10–12 minutes or until the edges are just starting to turn golden. Allow the cookies to cool completely on a wire rack.

Prepare the Pistachio Cream Filling:

• In a medium bowl, beat the softened butter until creamy. Gradually add the powdered sugar, then mix in the pistachio paste and vanilla extract.
• If the cream appears too thick, add milk one teaspoon at a time until you reach a smooth, spreadable consistency.

Assemble the Cookies:

• Pair up cookies of similar size. Spread a generous dollop of pistachio cream filling on the flat side of one cookie and sandwich it with its match.
• Repeat with the remaining cookies.

Serve and Store:

• Enjoy immediately or store in an airtight container for up to several days for the best flavor and texture.