Line the pan with parchment paper, leaving overhang on the sides for easy lifting later.

In a saucepan over medium heat, combine butter, sugar, milk, and salt. Bring to a gentle boil, stirring constantly, and cook briefly until the sugar dissolves fully.

Remove the saucepan from heat and stir in peanut butter and vanilla until smooth.

Fold the oats into the warm mixture, stirring until evenly coated and thick.

Transfer the mixture to the prepared pan and press firmly into an even layer. Compacting the mixture helps the bars hold together.

Melt chocolate chips with peanut butter until smooth. Spread evenly over the oat layer.

Refrigerate until firm, then lift out and slice into bars.