Whisk the flour, baking powder, and salt together in a bowl and set aside.
In a mixer fitted with the paddle attachment (or using a hand-held mixer), beat the butter on high speed until it is pale and fluffy.
Add the egg yolks and sugar and beat until the sugar is dissolved and the mixture is light.
Reduce the mixer speed to low and add the dry ingredients, mixing only until the ingredients are incorporated.
Turn the dough out onto a work surface and cut in half. Shape each half into a ball and wrap each ball in parchment or plastic. Freeze the dough for about 30 minutes, until firm.
Preheat the oven to 350°F. Prep a 9 x 12 inch baking pan by coating it with non-stick baking spray and lining it with parchment paper (make handles).
Remove one ball of dough from the freezer and grate the dough into the pan. Pat the dough gently into the corners and spread with the jam.
Grate the remaining dough over the jam and press it lightly to distribute evenly.
Bake the shortbread for about 40 minutes, or until golden brown.
Dust the top of the shortbread heavily with confectioner’s sugar as soon as you remove the pan from the oven.
Cool to room temperature on a rack. Dust with sugar again if you like.
Cut the shortbread into bars when it's cool.
