Step 1: Prepare the Tin
Begin by thoroughly lining your square baking tin with baking paper. Ensure the paper overhangs on two opposite sides; these “handles” will make it incredibly easy to lift the set rocky road out of the tin later. Smooth out any wrinkles for a neat finish. Set the tin aside.

Step 2: Melt the White Chocolate Base
Create a double boiler by placing a heatproof bowl over a saucepan of gently simmering water, ensuring the bottom of the bowl does not touch the water. Add the chopped white chocolate, cubed butter, and golden syrup to the bowl. Stir gently and continuously with a spatula until the mixture is completely smooth, glossy, and well combined. This gentle heat prevents the white chocolate from seizing. Remove the bowl from the heat once melted. Alternatively, you can melt this mixture in a microwave-safe bowl in 30-second bursts on medium power, stirring well between each burst.

Step 3: Combine with Festive Mix-Ins
Allow the melted chocolate mixture to cool for 2-3 minutes. This prevents the marshmallows from melting when added. Now, add all your prepared festive mix-ins to the bowl: the broken biscuit chunks, dried cranberries, chopped pistachios, and mini marshmallows. Using your spatula, fold everything together until every piece is evenly coated in the luxurious white chocolate mixture. The combination of red cranberries and green pistachios creates a wonderfully festive color palette.

Step 4: Press into the Tin and Set
Pour the combined white chocolate rocky road mixture into your prepared tin. Use the spatula, and then clean, lightly damp hands to press the mixture down firmly and evenly into all corners. A firm press ensures the slice holds together well when cut. For a decorative finish, scatter a few extra cranberries, pistachios, or mini marshmallows on top and press them in gently.

Step 5: Chill Until Firm
Place the tin in the refrigerator for at least 3-4 hours, or preferably overnight, to allow the rocky road to set completely. This no-bake slice relies on the white chocolate re-solidifying to hold its shape.

Step 6: Slice and Serve
Once fully set, use the parchment paper handles to lift the entire slab of White Christmas Rocky Road out of the tin and onto a cutting board. Using a large, sharp knife (wiping it clean with a hot cloth between cuts helps get clean slices), cut into squares or rectangles. For a festive touch, you can dust the top with a little icing sugar just before serving to resemble snow.