01 - Preheat the oven to 400°F. Line a baking tray with parchment paper and set aside.
02 - Roll out the puff pastry on a lightly floured surface and cut into 12 equal rectangles. Arrange the rectangles on the prepared tray, sprinkle evenly with granulated sugar, then place a second sheet of parchment paper and another baking tray on top to weigh them down and prevent excessive puffing.
03 - Bake for 15 to 20 minutes until the pastry rectangles are crisp and deeply golden. Transfer to a wire rack and let cool completely.
04 - In a mixing bowl, whisk the ricotta cheese until perfectly smooth. Add the 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, preserving 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. Top each with a second pastry rectangle, 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 for the best texture contrast.