Here is the recipe from that book with a few notes/changes that I have made.
1 pound (4 sticks) unsalted butter, room temperature
1 cup firmly packed light brown sugar
1 cup granulated sugar
2 teaspoons pure vanilla extract
3 and ¾ cups all purpose flour
1 cup almond flour or very finely ground almonds
1 and ½ cup blackberry preserves (I also just use whatever it takes to
cover the dish you're cooking it in)
½ cup chopped almonds
**last time I made it I put that much sugar in it, but it was too sweet. Not sure if it was the jam or there really was just too much sugar. So you may want to put 3/4 cup of each instead, or taste to your liking.
If you don’t have almond flour on hand, you can make it like I did by grinding up 1 cup of almonds in your food processor until they are finely ground. It’s going to be combined with the flour so texture-wise, you want to get it as finely ground as possible.
Combine the butter and sugars in a large bowl. Using an electric mixture set at medium low speed, beat it until creamy. Add the vanilla and salt and beat until combined.
Combine almond flour (or ground almonds) with the flour. Mix well. Combine the dry mixture into the butter mixture on low speed, until a smooth, soft dough forms. Spray a 9 by 13 inch baking pan with nonstick cooking spray and press 1/3 of the dough evenly into the pan to form a bottom crust. Wrap the remaining dough in plastic wrap and refrigerate until very cold and firm, at least 30 minutes. (Mine rarely makes it to 30 minutes. You can also put yours in the freezer, but make sure to thaw it properly in the fridge before baking.)
Preheat oven to 325 degrees Fahrenheit.
Bake the bottom crust until it is firm and just beginning to turn pale brown around the edges, about 20 minutes. 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 pan to the oven and continue baking until topping is firm and crisp and lightly golden in color, about 30 to 35 minutes. Let cool to room temperature.
Use a sharp knife to cut bars evenly into 15 large squares. Do not try to cut when it is cold. 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.
The bars will keep, covered tightly, for about 1 week at room temperature, or in the freezer for up to one month.