Grease a 9x9-inch square pan and set aside.

In a large saucepan over medium heat, melt butter. Stir in brown sugar and vanilla extract.

Mix in oats and cook over low heat for 2–3 minutes until well combined.

Press half of the oat mixture firmly into the bottom of the prepared pan. Reserve remaining half for topping.

In a small saucepan, melt chocolate chips and peanut butter over low heat, stirring until smooth.

Pour chocolate mixture over the oat crust and spread evenly.

Crumble remaining oat mixture over the top and gently press down.

Cover and refrigerate for 2–3 hours or until firm. Bring to room temperature before cutting into bars.