Preheat oven to 350°F. Butter and lightly flour a 9-by-13-inch baking pan.
Using an electric mixer on medium speed, cream butter and sugar until light and fluffy. Lower speed; add egg, vanilla and peanut butter and beat until combined.
In a separate bowl, sift flour, baking powder and salt. On low speed, slowly add flour mixture to peanut butter mixture. Mix until just combined. Set aside 1/2 cup dough.
Using your fingertips, press remaining dough into an even layer in pan. Spread preserves over dough. Crumble reserved 1/2 cup dough over preserves and then sprinkle with peanuts and peanut butter chips.
Bake until golden and bubbly, 45 minutes. Cool on a wire rack and cut into bars.
This recipe also appeared in the September 2007 issue.