Preheat oven to 400º F. On floured surface, roll out puff pastry to 11” x 16”.
Cut in half lengthwise and place both halves on an ungreased baking sheet. Pierce pastry with fork in several places.
Bake 7-10 minutes or until puffed and golden. Cool on rack. Blend confectioner’s sugar, cornstarch, egg yolks, sugar, vanilla and 2 tablespoons of the milk in medium bowl with a whisk. Set aside.
Bring remaining milk (3/4 cup plus 2 tablespoons) and 2 1/2 cups yogurt to a boil in a medium saucepan, while whisking. Stir hot milk-yogurt mixture into sugar, confectioner’s sugar, egg and cornstarch mixture and blend thoroughly.
Return to saucepan. Cook, stirring constantly, over medium heat for 4-5 minutes or until thickened to pudding consistency.
Remove from heat and stir in lemon zest. Refrigerate mixture for 20 minutes. On a clean surface or large cutting board, spread the thickened, slightly-cooled filling on one piece of the pastry.
Refrigerate additional 20 minutes, or until set.
Combine yogurt and confectioner’s sugar in small bowl.
Cover and refrigerate if not used immediately.
To assemble, place the plain piece of puff pastry on top of piece with filling on it. Frost. Keep chilled until ready to serve.
Before serving, slice into 10 bars. Top with berries, and if desired, dust with additional confectioner’s sugar.