Cream together the softened butter and powdered sugar until light and fluffy, about 3-5 minutes.
Add in the egg yolks and sour cream, mixing until well incorporated.
In another bowl, whisk together the flour, fine ground pistachios, baking powder, and baking soda. Gradually add this mixture to the wet ingredients, mixing until just combined.
Cover the dough with plastic wrap and refrigerate for at least 1 hour.
Preheat your oven to 180°C (350°F). Line your baking sheets with parchment paper. Roll out the dough to about 1/4-inch thick and cut out shapes.
Bake the cookies for 10-12 minutes, or until the edges are lightly golden. Let them cool on the baking sheets for a few minutes before transferring to a cooling rack.
In a mixing bowl, combine the softened butter, pistachio cream, orange blossom water, and vanilla extract. Beat until smooth and fluffy.
Once cooled, spread a generous amount of filling on one cookie and top with another to create a sandwich.
For ganache, melt the milk chocolate chips with the heavy cream and 1 tbsp of butter until smooth. Cool slightly before drizzling over the cookies.
