Preheat oven to 350. Grease and flour a 9 x 13 x 2 inch baking pan.
In the bowl of an electric mixer fitted with a paddle attatchment, cream the butter and sugar on medium speed until light yellow, about 2 minutes. With the mixer on low speed, add the vanilla, eggs, and peanut butter and mix untill well combined.
In a small bowl, sift together the flour, baking powder,and salt. With the mixer on low speed, slowly add the flour mixture to the peanut butter mixture. Mix just until combined.
Spread two thirds of the dough in the prepared pan, using a knife to spread it evenly. Spread the jam evenly over the dough. Drop small globs of the remaining dough evenly over the jam. Don't worry if all the jam is not covered, the dough will spread when it bakes. Sprinkle with the chopped peanuts and bake for 45 minutes. Cool and cut into small squares.