Line an 8x8 inch baking dish with parchment paper.

In a microwave-safe bowl, melt the white baking chips, stirring every 30 seconds until smooth and creamy.

In another bowl, heat the creamy peanut butter for about 30 seconds, then stir until silky. Combine it with the melted white chocolate.

Pour the mixture into the lined baking pan and smooth it out.

Melt the milk chocolate chips with the vegetable oil until glossy, then pour over the white chocolate mixture in zigzag lines.

Swirl the chocolate into the white mixture to create a marbled effect and cover with foil.

Chill in the fridge for about 45 minutes.

Remove from the fridge, lift out using parchment paper, and cut into 36 slices.

Serve on a decorative plate, optionally with vanilla ice cream or whipped cream.

Wrap any leftovers in an airtight container and store in the fridge for up to a week.