Preheat oven to 350°. Butter a 9″x 13″baking pan. Line bottom with parchment paper. Butter the parchment and dust with flour, tapping out the excess.
Beat butter and sugar together on medium speed of an electric mixer. Mix for about 2 minutes, until fluffy. Add eggs and peanut butter, and beat about 2 minutes or until combined.
In a separate bowl, whisk together flour, salt, and baking powder. Add to butter mixture and beat on low speed until combined. Add vanilla and mix.
Transfer two-thirds of dough to pan and spread evenly. Spread jam on top of dough. Crumble remaining dough on top of jam. Sprinkle with peanuts.
Bake for 45-60 minutes, or until golden. Rotate pan half-way through baking. Tent loosely with foil if bars are getting too dark.
Cool on a wire rack. Run a knife around the edges to loosen. Refrigerate 1-2 hours. Cut into bars and store in an airtight container at room temperature.
Makes about 3 dozen bars.