Step 1

Arrange a rack in the middle of the oven and heat to 350°F. Line the sides and bottom of a 9x13-inch baking pan (preferably metal, but glass will also work) with aluminum foil, then coat the foil with cooking spray or butter; set aside.

Step 2

Whisk the flour, baking powder, and salt together in a medium bowl; set aside.

Step 3

Place the butter and sugar in the bowl of a stand mixer fitted with the paddle attachment. Beat on low speed until combined, then increase the speed to medium-high and beat until lightened in color and creamy, about 3 minutes. Stop the mixer and scrape down the paddle and sides of the mixer with a rubber spatula.

Step 4

Add the peanut butter and beat on medium-high speed until combined, about 1 minute. Add the egg and vanilla and continue to beat until completely combined. Stop the mixer and scrape down the paddle and sides of the mixer with a rubber spatula.

Step 5

Return the mixer to low speed and gradually add the flour mixture, stopping when the flour is almost incorporated (do not overmix). Remove the bowl from the mixer and fold in the remaining flour by hand with the rubber spatula.

Step 6

Sprinkle 1/2 of the mixture in the baking pan and press into an even layer. Bake until the top is light golden-brown, 15 to 20 minutes.

Step 7

Dollop the jelly over the crust and spread into an even layer as best as you can without disturbing the crust. (Do not worry if the jelly doesn't spread much, it will melt in the oven.) Sprinkle evenly with the chopped peanuts, if using. Using your hands, crumble the remaining dough into pieces about the size of almonds and sprinkle evenly into the pan.

Step 8

Return the pan to the oven and bake until the top is golden-brown, about 20 minutes more. Remove the pan to a wire rack and let cool completely. To serve, grasp the foil in the middle of the pan and lift the bar cookie slab out of the pan and onto a cutting board. Cut into 32 bars.