In a large bowl, combine flour, sugar, salt, and lemon zest.
Add the cold butter and work the dough with your hands until it resembles coarse crumbs.
Add the whole egg and egg yolk, and knead briefly until a dough forms.
Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.
In a separate bowl, combine flour, sugar, and cinnamon.
Add the cold butter and rub it in with your fingers until you have a crumbly mixture.
Preheat oven to 350°F (175°C).
Roll out the dough on a lightly floured surface to about ⅛-inch thickness.
Cut out circles using a cookie cutter or a glass.
Place a spoonful of jam in the center of each circle.
Fold the dough in half over the jam to form a half-moon shape.
Press the edges together firmly to seal.
Place the pastries on a baking sheet lined with parchment paper.
Sprinkle generously with the streusel topping.
Bake for 20-25 minutes, or until golden brown.
Let cool slightly on the baking sheet before transferring to a wire rack to cool completely.