Line a bakers quarter sheet (or a 9x13 glass pan) with parchment paper or foil.
Put semi sweet chocolate chips in a small glass bowl. Microwave for 1 minute and stir gently until smooth. Set aside.
Pour vanilla chips in a medium sized glass bowl. Microwave for 1 minute 30 seconds. Stir gently until smooth. Add peanut butter and stir until well combined and smooth.
Pour vanilla-peanut butter mixture onto the prepared pan. Mixture won't reach the edges of the pan and that's OK. Once it's settled, take the melted semi sweet chocolate and pour it onto the vanilla-peanut butter mixture in lines.
Take a knife and run it the opposite direction of the chocolate lines you created, to achieve a swirl pattern. Run your knife through the mixture as much as you'd like, to create your desired swirl pattern.
Let cool either on the countertop or in the fridge. Cut into small squares. Store in an airtight container.