1½ cups all-purpose flour
½ teaspoon baking powder
¼ teaspoon salt
¾ cup creamy peanut butter
¾ cup firmly packed brown sugar
½ cup (1 stick) unsalted butter, at room temperature
1 teaspoon vanilla
¾ cup jelly or jam of your choice
2/3 cup coarsely chopped peanuts
Preheat oven to 350°F. Line an 8-inch square baking pan with heavy duty foil, leaving a 2-inch overhang around the edges and pressing firmly into corners and up sides of pan. Coat the foil with nonstick spray.
Whisk together the flour, baking powder, and salt in a medium bowl. Using an electric mixer, beat the peanut butter, sugar, and butter in a large bowl until smooth. Add egg and vanilla; beat on low speed until all ingredients are incorporated. Add flour mixture and beat on low speed until just blended.
Put half of the dough into prepared pan and put the remaining dough in the freezer for 10 minutes. With your fingertips, press the dough evenly into the bottom of the pan. Spread the jelly or jam evenly over the dough. Remove dough from freezer, and, using your fingertips, break into grape size pieces and scatter evenly over the jelly layer. Sprinkle chopped peanuts over.
Bake the bars until the top is golden brown, about 30 to 35 minutes. Cool completely in the pan. Using foil overhang as an aid, lift the bars from the pan. Gently peel back the foil from the edges. Cut into 25 squares.