http://www.gaylea.com/recipes/action/print/rec_id/209

In a large bowl, beat the butter with the sugar and egg yolk, using an electric mixer, for 2 minutes or until light and fluffy. In a separate bowl blend together flour, baking powder and salt until well combined.

Divide the dough into two equal portions and wrap tightly in plastic wrap. Freeze dough for 1 to 4 hours.

Preheat the oven to 350°F (180°C). Line a 9 x 13-inch (3 L) baking dish with parchment paper; reserve. Remove dough from freezer. Shred dough using a coarse grater or food processor, fitted with a metal shredding blade; replace one portion of shredded dough to the freezer.

Arrange remaining dough in an even layer in the prepared baking dish; lightly pat the dough down. Bake for 20 minutes or until lightly golden around the edges; cool for 20 minutes.

Meanwhile, blend the peanut butter with the icing sugar and butter until smooth and well combined. Spread the peanut butter mixture over the shortbread base in an even layer. Drop spoonfuls of the jam over the peanut butter and gently spread in an even layer.

Remove the remaining dough from the freezer and scatter over the jam layer. Bake for 20 to 25 minutes or until the top is set and lightly golden brown. Transfer pan to a wire rack and cool completely; cut into bars.

Makes 24 bars.

Tip: Try grape jelly or strawberry jam in place of the blueberry jam for a fun twist.