Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.

Roll out each sheet of puff pastry on a lightly floured surface to smooth any creases. Cut each sheet into rectangles, approximately 3 inches by 5 inches.

Place the rectangles on the prepared baking sheet. Prick the pastry with a fork to prevent it from puffing up too much during baking.

Bake the pastry in the preheated oven for about 15-20 minutes, or until golden brown and flaky. Remove from the oven and let cool completely.

While the pastry cools, prepare the cream filling. In a mixing bowl, whip the heavy cream until soft peaks form.

Gradually add the powdered sugar and vanilla extract to the whipped cream, continuing to whip until stiff peaks form.

In another bowl, mix the milk and pistachio paste until well combined. Gently fold this mixture into the whipped cream until fully incorporated.

Once the puff pastry has cooled, take one rectangle and spread a layer of the pistachio cream filling on top. Sprinkle some finely chopped pistachios over the cream.

Top with another rectangle of puff pastry and repeat the layering process, adding more cream and pistachios.

Finish with a third layer of puff pastry on top. Optionally, dust the top with powdered sugar and garnish with extra chopped pistachios.

Refrigerate the mille-feuille for at least 1 hour before serving to allow the flavors to meld and the cream to set.

Slice into portions and serve chilled. Enjoy your delightful pistachio and cream mille-feuille!