For the Base:

1. Prepare the Baking Tin: Line an 8-inch square baking tin with parchment paper, leaving some overhang to make it easier to lift the tray bake out later.
2. Crush the Biscuits and Maltesers: Place the digestive biscuits in a plastic bag and crush them with a rolling pin until they form fine crumbs. Crush the Maltesers separately, leaving some larger chunks for added texture.
3. Melt the Chocolate and Butter: In a heatproof bowl set over a saucepan of simmering water, melt the milk chocolate and butter together, stirring until smooth. Remove from the heat and stir in the golden syrup.
4. Combine the Ingredients: In a large mixing bowl, combine the crushed biscuits and Maltesers. Pour the melted chocolate mixture over the top and stir until all the dry ingredients are well coated.
5. Press into the Tin: Pour the mixture into the prepared baking tin and press it down firmly with a spatula to create an even layer.

For the Topping:

1. Melt the Chocolate: Melt the milk chocolate in a heatproof bowl set over simmering water until smooth and glossy.
2. Top the Tray Bake: Pour the melted chocolate over the biscuit base, spreading it evenly with a spatula. Sprinkle the remaining Maltesers over the top, pressing them lightly into the chocolate.
3. Chill the Tray Bake: Place the tray in the fridge to chill for at least 2 hours, or until the chocolate topping is fully set.
4. Serve: Once set, use the parchment paper overhang to lift the tray bake out of the tin. Cut into squares and serve.