Melt butter and brown sugar in large saucepan over medium heat, until the butter has melted and the sugar has dissolved. .
Stir in vanilla and oats and cook for a couple of minutes.
Line a 9-inch baking dish with parchment paper.
Spread half of the oat mixture into the baking dish and press down.
Melt the peanut butter and chocolate chips together in a bowl and stir until it’s smooth then pour over the prepared mixture. (Save just a little bit for drizzling)
Press the rest of the oat mixture onto the top of the chocolate layer and then drizzle with the rest of the chocolate.
Refrigerate for an hour and then cut into bars. (It's easier to cut them if you let them thaw out for a few minutes first)
