1. Preheat oven to 375°F and line a baking sheet with parchment paper.

2. Grind pistachios in a food processor until fine. Set aside.

3. Cream butter, powdered sugar, vanilla sugar, and salt until smooth.

4. Add egg and ground pistachios and mix well.

5. Gradually add flour and baking powder and knead until smooth dough forms.

6. Roll dough on a floured surface to just under 1 cm thick. Cut out shapes with a cookie cutter.

7. Bake 10 to 12 minutes until lightly golden at edges. Cool completely on a wire rack.

8. Spread pistachio paste on flat side of one cookie and press another on top to form sandwiches.

9. Melt white chocolate over a double boiler, stirring until completely smooth.

10. Dip each sandwich cookie into the melted white chocolate. Place on parchment paper.

11. Decorate with drizzled white chocolate, chopped pistachios, and edible rose petals.

12. Allow to set completely before serving.