Melt the milk or dark chocolate in a large heatproof bowl set over a pan of simmering water. Remove from the heat, then melt the white chocolate in the same way. Or, melt the chocolates in the microwave in short bursts.

Line a baking tray or sheet with baking parchment. Use a baking sheet if you want thinner shards of bark, or a smaller tray for fewer, chunkier pieces.

Pour the melted milk or dark chocolate over the prepared sheet or tray, then tip side to side to spread the chocolate out to your desired shape and thickness. Spoon over teaspoonfuls of the white chocolate, reserving a little, then use the tip of a knife or a skewer to swirl the white chocolate through the milk or dark.

Scatter over the biscuit pieces, then drizzle over the remaining white chocolate in a spiral pattern. Scatter over the sprinkles, nuts or sweets, then leave in a cool place to set fully. Cut or break into pieces and wrap.