- 2 cups unsalted butter, softened
- 4 egg yolks
- 4 cups all-purpose flour
- 2 cups white sugar
- 2 teaspoons baking powder
- 1 teaspoon ground cardamom
- 1/3 teaspoon salt
- 1 cup blackberry jam, at room temperature
- 1/4 cup confectioners' sugar
- Beat butter in a bowl with an electric mixer until light and fluffy. Add egg yolks to butter one at a time, blending well after each addition.
- Mix flour, white sugar, baking powder, cardamom, and salt together in a bowl. Stir flour mixture into butter mixture until just combined. Divide dough in half and wrap each tightly in plastic wrap. Freeze for at least 3 hours.
- Preheat oven to 350 degrees F (175 degrees C).
- Grate 1 ball of frozen dough evenly into the bottom of a 9×13-inch baking pan. Spread blackberry jam over grated dough, leaving 1/2-inch space around the edges. Grate the second ball of frozen dough over the jam.
- Bake in the preheated oven until golden brown, 30 to 40 minutes. After shortbread cools, sprinkle with confectioners' sugar and cut into bars.