Grease a 9×9 inch square pan.

In a large saucepan over medium heat, melt the butter.

Stir in the brown sugar and vanilla extract until combined.

Mix in the quick cooking oats.

Cook over low heat for 2 to 3 minutes, stirring often, until the ingredients are well blended.

Press half of the oat mixture firmly into the bottom of the prepared pan.

Reserve the remaining oat mixture for the topping.

In a small heavy saucepan over low heat, melt the chocolate chips and peanut butter together.

Stir frequently until the chocolate mixture is smooth.

Pour the chocolate peanut butter mixture over the oat crust in the pan.

Spread the chocolate layer evenly with a knife or the back of a spoon.

Crumble the remaining oat mixture over the chocolate layer.

Press the topping gently so it sticks to the chocolate layer.

Cover the pan and refrigerate for 2 to 3 hours, or overnight, until firm.

Let the bars sit at room temperature for a few minutes before cutting into squares.