Preheat oven to 350°. Line an 8-inch square baking pan with parchment paper or foil, letting excess extend over sides of pan. Spray with baking spray with flour.

In a large bowl, beat ¾ cup peanut butter and butter with a mixer at medium speed until creamy. Beat in egg and vanilla.

In a medium bowl, whisk together flour, brown sugar, ½ cup peanuts, oats, baking powder, and salt. Gradually add flour mixture to peanut butter mixture, beating until combined. (Dough will be thick.) Reserve 1 cup dough. Press remaining dough into bottom of prepared pan. Spread pepper jelly onto dough. Drop remaining ¼ cup peanut butter by teaspoonfuls over jelly. Crumble reserved 1 cup dough over jelly and peanut butter. Sprinkle with remaining ¼ cup peanuts.

Bake until golden brown, about 30 minutes. Let cool completely on a wire rack, about 6 hours. Using excess parchment or foil as handles, remove from pan, and cut into bars.