1-Preheat oven to 350°F and line an 8×8-inch metal baking pan with parchment paper for easy removal.

2-Whisk together the flour, baking soda, and salt in a medium bowl to blend the dry ingredients evenly.

3-In a mixer or bowl, combine melted butter and peanut butter until smooth, creating a creamy base for the dough.

4-Mix in brown sugar and granulated sugar until well combined, which adds moisture and sweetness to the mixture.

5-Add vanilla extract and egg, mixing for about 2 minutes to fully incorporate and develop the flavor.

6-Gradually add dry ingredients on low speed, mixing just until combined; the dough will be soft and slightly crumbly at this stage.

7-Stir in optional mix-ins by hand, if desired, like chocolate chips or nuts for added texture.

8-Press dough evenly into the prepared pan to ensure uniform baking and a consistent chewy result.

9-Bake for 20 to 22 minutes, keeping an eye on them to avoid overbaking for that soft center.

10-Cool in the pan for 10 minutes, then transfer to a cooling rack to cool completely before cutting.

11-Cut into bars and serve, enjoying the fresh, homemade taste right away.