Preheat the oven to 350°F (175°C). Grease a 9x9-inch baking pan thoroughly, ensuring the corners are coated to prevent sticking.
Cream the base mixture
In a mixing bowl, beat together the peanut butter and softened butter until smooth and well blended.
Incorporate sugars and wet ingredients
Gradually add the brown sugar, granulated sugar, eggs, and vanilla extract into the peanut butter mixture. Beat until the batter is fluffy and well combined.
Add dry ingredients
In a separate bowl, combine the flour, baking soda, and salt. Slowly fold the dry mixture into the peanut butter batter until fully incorporated.
Bake
Pour the batter into the prepared pan and spread evenly. Bake for 30–35 minutes, or until the top is golden and springs back gently when touched. A toothpick inserted in the center should come out with a few moist crumbs.
Cool and slice
Remove from the oven and allow the brownies to cool completely in the pan. Once cooled, cut into 16 even squares and serve.
Notes
To make these Peanut Butter Brownies gluten-free, substitute the all-purpose flour with a 1:1 gluten-free baking blend. Verify that the baking soda, peanut butter, and other ingredients are labeled gluten-free to avoid cross-contamination.