In a food processor, or by hand, combine all of the pastry ingredients until dough forms. Do not overwork. Divide into two balls - one double the size of the other. Refrigerate for at least 2 hours.

Preheat oven to 420F. Roll out the larger ball of dough into a rectangle on a piece of parchment paper to about a fifth of an inch thickness.

Spread jam over the dough, leaving a slight border. Then, use a large grater to grate the remaining ball of dough on top of the jam to make the "topping."

Bake for approximately 20 minutes. Let cool, then cut into square bars and sprinkle with confectioner's sugar, if desired.