01 - Preheat the oven to 400°F (200°C). Line a baking tray with parchment paper.
02 - Roll out the puff pastry on a lightly floured surface and cut into 12 equal rectangles. Arrange on the prepared tray, sprinkle evenly with granulated sugar, then place a second sheet of parchment paper and another baking tray on top to prevent excessive puffing during baking.
03 - Bake for 15 to 20 minutes until the pastry is crisp and golden brown. Transfer to a wire rack and let cool completely.
04 - In a mixing bowl, whisk the ricotta cheese until smooth and creamy. Add the sifted powdered sugar, lemon zest, lemon juice, and vanilla extract, then mix thoroughly until well combined.
05 - In a separate chilled bowl, whip the heavy cream to stiff peaks. Gently fold the whipped cream into the ricotta mixture in two additions, maintaining as much volume as possible. Refrigerate until ready to assemble.
06 - Spread or pipe a generous layer of lemon ricotta cream onto six of the pastry rectangles. Place a second pastry rectangle on top of each, pressing gently to create a sandwich.
07 - Dust the top layer of each assembled mille feuille with powdered sugar and garnish with fresh lemon zest. Serve immediately to maintain pastry crispness.