Preheat oven to 350 degrees F. Grease a 9x13-inch pan with butter and line the bottom with waxed paper. Grease the waxed paper and coat the inside of the pan with flour.
Place butter and sugar in a bowl. Beat on medium-high heat until fluffy, about 2 minutes. Add eggs, peanut butter and vanilla, and beat for 2 additional minutes, until combined.
Stir flour, salt and baking powder together. Add to moist ingredients and mix well.
Spoon 2/3 of mixture into prepared pan and spread evenly. Next, evenly spread jam on top of peanut butter mixture. Then, take small amounts of remaining dough and scatter randomly over top, trying to cover most of the surface. Sprinkle with chopped peanuts.
Bake approximately 45 minutes or until top is golden. Remove from oven and let cool completely before cutting.