Line a large baking sheet with parchment paper or a silicone baking mat. Ensure it is completely dry.

Place white chocolate (and oil if using) in a microwave-safe bowl. Microwave at 50% power in 30-second intervals, stirring in between, until fully melted and smooth.

Pour the melted chocolate onto the prepared baking sheet.

Use a spatula to spread the chocolate into an even layer, approximately 1/4 inch thick.

Immediately scatter the pastel M&Ms and sprinkles over the wet chocolate. Press down gently to secure.

Allow to set at room temperature for 1-2 hours, or refrigerate for 20 minutes to speed up the process.

Once hardened, break into shards using your hands. Store in an airtight container.