Prep the pan: Line an 8-inch (20 cm) square baking pan with parchment paper, leaving an overhang for easy lifting later.
Melt the base: In a heatproof bowl set over a pan of barely simmering water, melt the milk chocolate, butter, and golden syrup. Stir often until smooth.
Do not let water touch the chocolate bowl.
Cool slightly: Remove the bowl from heat and let the mixture cool for 5–7 minutes. It should be glossy but not hot, so the marshmallows don’t melt.
Crush and combine: In a large bowl, add the crushed biscuits, mini marshmallows, and 1 cup (about 160 g) of mini eggs. Add nuts and dried fruit if using.
Sprinkle in a pinch of salt.
Mix with chocolate: Pour the cooled chocolate mixture over the dry ingredients. Fold gently with a spatula until everything is evenly coated.
Press into pan: Tip the mixture into the lined pan. Press firmly and evenly with the back of a spoon.
Scatter the remaining mini eggs on top, lightly pressing them into the surface.
Optional drizzle: Melt the white chocolate and drizzle over the top for a contrast finish.
Chill to set: Refrigerate for at least 2 hours, or until firm. For clean slices, chill 3–4 hours.
Slice and serve: Lift out using the parchment. Use a sharp, warmed knife to cut into 16 squares.
Wipe the blade between cuts for neat edges.
