Preheat oven to 350 F. Line an 8 X 8-inch baking pan with parchment paper using only one piece so none of the filling leaks out during the baking process.
In a bowl, whisk together flour, sugar & salt to combine. With a pastry cutter, cut in cold butter, adding vanilla & lemon zest. Transfer dough to prepared baking pan. Using your finger tips, evenly press the dough onto the bottom of the pan.
Carefully prick the bottom of the crust with the tines of a fork making sure not to make any holes in the parchment. Bake for about 20 minutes or just until a pale golden color. Remove from oven & place on a wire rack to cool while you prepare the filling.
In a bowl, beat together butter & sugar with a hand mixer until light & fluffy. Beat in eggs until incorporated then the corn syrup & vanilla. Stir in flour, salt & baking powder.
Sprinkle 100 gm of the pumpkin seeds & all of the dried cranberries over the baked shortbread base. Then pour the filling over this mixture & bake for about 20-25 minutes or until filling is set. Remove from oven & place on a wire rack to cool. Sprinkle remaining 20 gm of pumpkin seeds on top for decoration. Serve at room temperature or chilled (or straight from the freezer).