Chocolate Shortbread Sandwich Bars

Pre-heat over to 350.
Butter a 9-by-13-inch baking pan.
Cut a piece of parchment paper to fit the bottom of the pan.
Butter the paper.
In a mixing bowl with a wooden spoon, cream the butter.
Add the granulated sugar a little at-a-time until it is well blended.
Beat in the egg yolks and vanilla.
Sift together the flour, baking powder, and salt.
Stir the dry mixture into the butter mixture a littlt-at-a-time until it is incorporated.
The dough will be sticky.
Place 2/3's of the dough in the pan.
Using your fingers press it into an even layer.
Flour your hands as you work.
Prick the dough all over with a fork.
Sprinkle the chocolate chips (or pieces) over the dough to within 1/4" of the edges.
Place clumps of the remaining dough around the perimeter of the chocolate, making a 1/2" border.
Then scatter the remaining dough clumps to fill in the rectangle.
You will still be able to see chocolate through the dough.
With a lightly floured hand, pat the clumps gently all over to flatten them slightly.
Sprinkle the dough lightly with the granulated sugar.
Bake for 25 to 30 minutes or until the top of the pastry is pale golden.
Remove the pan from the oven and set it on a wire rack to cool.
Cover the pan with foil and refrigerate just until the chocolate sets.
Remove from the refrigerator and cut the pastry into bars, making 3 horizontal cuts and 4 vertical cuts.
Lift our the bars and sprinkle them with confectioners' sugar, and stack on a serving plate.