How to Make It
In a medium bowl, whisk the 3 flours with the baking powder, cinnamon and salt. In a stand mixer fitted with the paddle, beat the butter with the granulated sugar, lemon zest and vanilla at medium speed until smooth, about 5 minutes. Beat in the egg yolks one at a time, scraping down the side of the bowl, until incorporated. Beat in the dry ingredients at low speed until the dough just comes together. Press one-third of the dough and two-thirds of the dough into 2 disks and wrap in plastic. Refrigerate overnight until firm.
Preheat the oven to 350°. Coat a 9-by-13-inch metal baking pan with cooking spray. Line with parchment paper, leaving a 2-inch overhang on the 2 long sides, and coat with cooking spray. Using the large holes of a box grater, shred the larger disk of dough evenly in the pan.
Spread the jam over the shredded dough, leaving a 1/2-inch border. Shred the smaller disk over the jam. Bake, rotating the pan halfway through, for 35 to 45 minutes, until the top is deep golden brown. Transfer to a wire rack and let cool. Refrigerate in the pan until firm, at least 2 hours.
Using the paper, transfer the pastry to a work surface. Dust with confectioners’ sugar, cut into 2-inch bars and serve cold or at room temperature.