Place the lemon zest in a medium bowl and set aside. Spoon 4 tablespoons of the lemon juice into a very small bowl, sprinkle with the gelatin and set aside to thicken and almost set.

Place the eggs, egg yolks, sugar, salt, and remaining lemon juice in the bowl with the lemon zest and whisk together.

  Pour into a saucepan, add the butter and cook over med-low heat, whisking constantly, until the custard begins to thicken.   Just before boiling remove from the heat and add the now thickened lemon gelatin mixture. Pour the whole mixture through a fine mesh strainer set over a medium bowl.   Cover the surface directly with plastic wrap and chill overnight until set quite firm

Preheat oven to 425°F/220°C. Line 2 baking sheets with parchment paper or plain brown paper; set aside.

Unfold puff pastry sheet and trim edges to a 9-inch square. Cut pastry into nine 3-inch squares. Transfer pastry squares to the prepared baking sheets; prick pastry.

  Bake in a preheated oven for 18-23 minutes, or until golden. (Or bake according to package directions.) Carefully remove pastries from baking sheet. Cool on a rack

In a medium mixing bowl combine confectioners' sugar and vanilla. Stir in enough boiling water to make a glaze of spreading consistency; set aside.

To Assemble =
Use the tines of a fork to separate each pastry square horizontally into 3 layers