1 lb unsalted butter, at room temperature
1 c firmly packed light brown sugar
1 c white sugar
2 t vanilla extract
1 t salt
3 ¾ c unbleached all purpose flour
1 c almond flour or very finely ground almonds
1 ½ c blackberry preserves
½ c chopped almonds
confectioners’ sugar for dusting
Combine the butter and sugars in a large bowl.
Beat until creamy, using an electric mixer set at med-low speed.
Add the vanilla and salt and beat until combined.
Beat the flours into the butter mixture on low speed, just until a smooth, soft dough forms.
Spray a 9x13 in baking pan with nonstick cooking spray and press one third of the dough evenly into the pan to form a bottom crust.
Wrap the remaining dough in a plastic wrap and refrigerate until very cold and firm, at least 30 mins.
Position a rack in the middle of the oven and preheat to 325 degrees.
Bake the bottom crust until it is firm and just beginning to turn pale brown around the edges, about 20 mins.
Remove the pan from the oven and spread the preserves, evenly over the crust.
Crumble the remaining shortbread dough over the jam to form a pebbly, crumbled topping.
Sprinkle with the chopped almonds.
Return the pan to the oven and continue baking until topping is firm and crisp and lightly golden in color, about 30 mins.
Transfer to a wire rack and let cool to room temperature.
Use a sharp knife to cut bars evenly into 15 large squares.
Remove the bars from the pan with a metal spatula and, if desired, cut in half on the diagonal to form 30 smaller triangular bars.
Dust with confectioners’ sugar and serve.