1 cup (2 sticks) unsalted butter, room temperature, plus more for pan
3 cups all-purpose flour, plus more for pan
1 1/2 cups sugar
2 large eggs
2 1/2 cups smooth peanut butter
1 1/2 teaspoons salt
1 teaspoon baking powder
1 teaspoon pure vanilla extract
1 1/2 cups strawberry jam, or other flavor
2/3 cups salted peanuts, roughly chopped
Heat oven to 350 degrees.
Grease a 9x13 inch pan with butter, and line the bottom with parchment paper.
Grease the parchment, and coat inside of pan with flour; set aside.
Place butter and sugar in the bowl of an electric mixer fitted with the paddle attachment.
Beat on medium-high speed until fluffy, about 2 minutes.
On medium speed, add eggs and peanut butter; beat until combined, about 2 minutes.
Whisk together salt, baking powder, and flour.
Add to bowl of mixer on low speed; combine.
Transfer two-thirds of mixture to prepared pan; spread with offset spatula.
Using offset spatula, spread jam on top of peanut butter mixture.
Dollop remaining third of peanut butter mixture on top of jam.
Sprinkle with peanuts.
Bake until golden, about 45 minutes.
Transfer to a wire rack to cool; cut into about thirty-six 1 1/2 by 2 inch pieces.