Preheat your oven to 350°F (175°C) and grease a 9x9-inch baking pan or line it with parchment paper for easy removal.
In a medium mixing bowl, combine the creamy peanut butter, brown sugar, and granulated sugar. Mix until smooth and well blended.
Add the egg and vanilla extract to the peanut butter mixture, stirring until fully incorporated.
Sprinkle the baking powder and salt into the mixture, followed by the flour. Mix until just combined—do not overmix.
Gently fold in the semi-sweet chocolate chips and chopped peanuts if using, ensuring an even distribution.
Pour the batter into the prepared baking pan, smoothing it out evenly with a spatula.
Bake in the preheated oven for about 20-25 minutes, or until the edges are lightly golden and a toothpick inserted in the center comes out mostly clean (some moist crumbs are fine).
Allow the blondies to cool in the pan for 10-15 minutes before lifting them out (if using parchment) and transferring to a wire rack. Let them cool completely before cutting into squares.
Notes
Serve warm with melted peanut butter and sea salt for an elevated touch.