Line an 8-inch or 9-inch square baking dish with parchment paper, allowing some overhang on the edges.

In a medium saucepan over medium heat, combine ½ cup of butter and 1 cup of brown sugar. Stir frequently until melted.

Add 1 teaspoon of vanilla extract and mix well.

Stir in 3 cups of rolled oats, reduce heat to low, and cook for 3-4 minutes, stirring constantly.

Pour half of the oat mixture into the lined baking dish, pressing evenly to form a solid crust.

In a microwave-safe bowl, combine 1 cup of chocolate chips and ½ cup of peanut butter. Microwave in 30-second increments, stirring until smooth.

Pour the melted chocolate and peanut butter mixture evenly over the pressed oat base.

Spoon the remaining oat mixture over the chocolate filling, pressing gently to create a uniform topping.

Refrigerate the bars for 2-3 hours or overnight until fully set.

Remove the bars using parchment paper overhang, cut into squares or bars, and enjoy.