Step 1

In a medium bowl, whisk together the flour, baking powder, salt, set aside.

Step 2

Add the butter to the bowl of a stand mixer fitted with the paddle blade (or, better, a scraper blade) and beat on medium speed until pale and fluffy (5 to 8 minutes). Add the sugar and mix until dissolved. Add the egg yolks and almond extract, and continue beating until completely incorporated.

Step 3

Reduce speed to low and slowly add the dry ingredients. Mix only until incorporated (do not over mix).

Step 4

Turn the dough out on you cutting board, gather up into a mass, and then cut the dough in half. Form each half into a ball*, and wrap each in plastic wrap. Freeze the dough for at least 30 minutes, until firm.

Step 5

Preheat oven to 350°F with rack in the center position.

Step 6

Remove one ball of dough from the freezer and grate the dough using a box grater into a 9" x 12" baking pan (use the large hole side).

Step 7

Gently pat the dough shreds to even it out in the pan, pushing the shreds into the corners. Spread the jam or preserves over the top. If the jam is hard to spread, heat briefly in the microwave and stir well. You might not need all two cups: use your judgment.

Step 8

Grate the second ball of dough over the jam, and pat to even out the surface.

Step 9

Bake for 40 minutes, until the shortbread is golden. Remove from oven, and immediately dust with confectioner's sugar through a sifter or small sieve. Allow the shortbread to cool in the pan, set on a rack. Cut into squares or triangles, and serve. Store, covered, at room temperature.