Prep the pan: Line an 8-inch (20 cm) square tin with parchment, leaving overhang for easy lifting.
Melt the base: In a heatproof bowl, combine chocolate, butter, and golden syrup.
Microwave in 20β30 second bursts, stirring until smooth, or melt over a gentle bain-marie. Stir in vanilla and a pinch of salt.
Cool slightly: Let the chocolate mixture sit for 3β4 minutes so itβs warm, not hot. This helps prevent the marshmallows from melting.
Mix the goodies: Fold in crushed biscuits, marshmallows, and mini eggs.
Reserve a handful of eggs for the top. Gently fold in halved mini Creme Eggs so they keep their shape.
Press and top: Scrape the mixture into the lined tin and press it into an even layer. Scatter the reserved mini eggs and Creme Egg halves on top.
Add sprinkles or extra biscuit crumbs if you like.
Chill: Refrigerate for 2β3 hours, or until firm enough to slice cleanly.
Slice: Lift out using the parchment. Use a sharp knife warmed under hot water and dried to cut into 16 squares. Wipe the knife between cuts for neat edges.