Preheat your oven to 350°F. Line an 8x8-inch baking dish with parchment paper and lightly grease the paper.

In a bowl, whisk melted butter, brown sugar, and granulated sugar until smooth. Add egg and vanilla, mixing well.

Stir in the peanut butter until the mixture is fully combined.

Add the salt, all-purpose flour, and baking powder. Gently fold the mixture until just combined; do not overmix.

Carefully pour the batter into your prepped pan and spread it out evenly. Bake for approximately 20-25 minutes, or until a toothpick inserted into the center comes out mostly clean.

Allow the blondies to cool completely in the pan. Use the parchment paper overhang to lift them out, then cut into squares and serve.