Line an approximately 28 × 18cm brownie tin or similar-sized dish with baking paper.
Break the chocolate into smaller pieces and melt using either a bain-marie or microwave. Bain-marie: Place the chocolate in a heatproof bowl over a saucepan of gently simmering water, making sure the bottom of the bowl doesn't touch the water. Stir until smooth. Microwave: Heat the chocolate in 15-second bursts, stirring between each one, until completely melted and smooth. Cool the chocolate down for a few minutes before adding to the rest of the ingredients. You do this by stirring the chocolate gently. Don't let it set too hard though.
Add the marshmallows, peanuts and chopped lollies to a large bowl.
Pour over the warm melted chocolate and gently fold everything together until evenly coated.
Transfer the mixture to the prepared tin and spread into an even layer. Don't spread it too thinly if you prefer chunkier pieces.
Add festive sprinkles, if using, then refrigerate for 3–4 hours or until completely firm.
Once set, remove from the tin and cut into approximately 15–18 pieces. Serve chilled or allow it to come towards room temperature before serving if you prefer a slightly softer texture.