Make the shortbread base

• Heat the oven to 180°C and grease and line a baking tray.
• Rub the softened butter into the sifted flour with the caster sugar until it forms a soft dough.
• Press the dough evenly into the lined tray and prick all over with a fork.
• Bake for 20 min until pale golden, then set aside to cool.

Cook the caramel

• Tip the condensed milk and golden syrup into a saucepan with the remaining butter.
• Heat gently, stirring constantly, until the butter melts and the mixture is smooth.
• Keep stirring over a medium heat until the caramel thickens and turns a deep golden colour.
• Pour the caramel over the cooled shortbread and spread level, then chill until firm.

Add the chocolate topping

• Melt the milk chocolate in a bowl over a pan of simmering water, or in short bursts in the microwave.
• Pour the melted chocolate over the set caramel and spread it right to the edges.
• Scatter over the crushed and whole Maltesers, pressing them lightly into the chocolate.
• Finish with a pinch of flaky sea salt.

Chill and slice

• Chill the tray in the fridge until the chocolate is fully set.
• Cut into squares with a warm knife and serve.