2 1/4 cups all-purpose flour (spooned and leveled)
1 cup sugar
1 cup (2 sticks) unsalted butter, room temperature
1/2 teaspoon fine salt
1 large egg, lightly beaten
1 teaspoon pure vanilla extract
1 jar (12 ounces) grape jelly
3/4 cup chopped roasted salted peanuts
1/2 cup peanut butter chips
Preheat oven to 375 degrees. Brush a 9-inch square baking pan with butter and line with parchment paper, leaving a 2-inch overhang on two sides. Butter parchment.
In a large bowl, whisk together flour, sugar, and salt. With a pastry cutter or your hands, work in butter until mixture resembles coarse meal with a few pea-size pieces of butter remaining. Add egg and vanilla extract; stir until dough just comes together. Set aside 1 cup dough and firmly press remaining dough into pan in an even layer. Using a small offset spatula, spread grape jelly over top.
Combine reserved dough, peanuts, and peanut butter chips; crumble over jam layer. Bake until topping is deep golden brown, 45 to 50 minutes. Let cool completely in pan on a wire rack. Run a sharp knife around edges, then, using parchment, lift cake from pan and cut into 12 squares.