How to Make It
Heat oven to 350° F. Spray an 8-inch square baking pan with the cooking spray. Line the pan with a piece of parchment, leaving an over-hang on two sides; spray the parchment with the cooking spray.
In a medium bowl, whisk together the flour, salt, cinnamon, and nutmeg.
Using an electric mixer, beat the butter and sugar on medium-high speed until fluffy, 2 to 3 minutes. Beat in the egg yolks and vanilla. Reduce speed to low and gradually add the flour mixture, mixing until just combined (do not overmix).
Transfer two-thirds of the dough to the prepared pan and press in evenly; spread the jam on top. Crumble the remaining dough over the jam and sprinkle with the walnuts. Bake until golden, 35 to 45 minutes. Cool completely in the pan.
Holding both sides of the paper overhang, lift the cake out of the pan, transfer to a cutting board, and cut into 24 rectangles (6 rows by 4 rows). Store the bars in an airtight container at room temperature for up to 5 days.