01 - Preheat the oven to 400°F. Line two baking sheets with parchment paper.
02 - Lay the puff pastry sheets flat on the prepared baking sheets. Prick the surfaces thoroughly with a fork to prevent excessive rising during baking. Top each sheet with another piece of parchment paper and place a second baking sheet on top to weigh them down and ensure even, flat baking.
03 - Bake for 15 to 18 minutes until the pastry turns a deep golden brown and feels crisp. Remove the top baking sheet and parchment, then allow the pastry to cool completely on the pans.
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 the mixture is completely smooth and free of lumps.
05 - In a separate bowl, whip the heavy cream using an electric mixer or whisk until soft peaks hold their shape. Gently fold the whipped cream into the lemon ricotta mixture in two additions, being careful not to deflate the cream. Refrigerate until ready to assemble.
06 - Once the pastry sheets are completely cool, carefully trim any uneven edges with a sharp knife. Cut each sheet into 3 equal rectangles, yielding 6 total pastry layers.
07 - Place one pastry rectangle on a serving plate. Spread one-third of the lemon ricotta filling evenly over the surface using an offset spatula. Top with a second pastry rectangle and spread another third of the filling. Finish with a third pastry rectangle, placing it on top. Repeat to build a second mille feuille with the remaining layers and filling.
08 - Lightly dust the top of each assembled mille feuille with powdered sugar. Garnish with lemon zest curls if desired.
09 - Refrigerate for at least 30 minutes before slicing to allow the filling to set. Serve cold for the best texture and clean presentation.