First, beat together the sugar, butter, vanilla, eggs, and orange zest until it becomes pale yellow in color.
Then, add the flour and baking powder and mix together by hand, rubber spatula, or with a paddle attachment.
Reserve half the dough to be grated for the topping of the bar and the other half as the base.
Place the reserved dough for the topping in a ziplock and into the freezer for 15 minutes.
Preheat oven to 350 F.
Spread out the remaining dough into a thin layer onto a lightly greased 9 by 13 baking pan.
Spread all the jam evenly on top of that layer leaving 1 inch around all the edges.
Grate the dough that was placed in the freezer on top of the jam layer covering the jam. It gives it a streusel look/effect.
Bake in the oven for 25 minutes on the bottom rack then another 10 min on the tap rack.
Cool and sprinkle with powdered sugar and cut into 16 even bars!