01 - Preheat the oven to 400°F. Line two baking sheets with parchment paper.
02 - Place the puff pastry sheets onto the prepared baking sheets. Prick the dough all over with a fork to prevent excessive puffing. Cover each sheet with another piece of parchment paper and place a second baking sheet on top to weigh it down during baking.
03 - Bake for 15 to 18 minutes until the pastry is golden brown and crisp. Remove the top baking sheet and parchment layer, then allow the pastry to cool completely.
04 - While the pastry cools, combine the ricotta cheese, powdered sugar, lemon zest, lemon juice, and vanilla extract in a medium mixing bowl. Whisk until smooth and creamy.
05 - In a separate bowl, whip the heavy cream until soft peaks form. Gently fold the whipped cream into the lemon ricotta mixture until fully incorporated. Refrigerate until ready to assemble.
06 - Once the pastry sheets are completely cool, carefully trim the edges and cut each sheet into 3 equal rectangles, yielding 6 total pieces.
07 - Place one pastry rectangle on a serving plate. Spread one-third of the lemon ricotta filling evenly over the top. Add a second pastry layer and spread another third of the filling. Finish with the third pastry layer on top. Repeat with the remaining pastry rectangles and filling to build a second mille feuille.
08 - Lightly dust the top of each assembled mille feuille with powdered sugar. Garnish with lemon zest curls if desired. Chill for at least 30 minutes before slicing to allow the layers to set. Serve cold.