Preheat oven to 180°C (160°C fan) mark 4. Grease and line a 20.5cm (8in) square tin with baking parchment.

Melt butter and both chocolates in a medium pan over low heat. Take off heat and leave to cool slightly.

Beat in eggs one at a time, then mix in sugar followed by the malted drinking powder, flour, baking powder and ¼tsp fine salt. Finally, mix in Maltesers. Scrape into prepared tin and bake for 45min, or until set with only a slight wobble.

Cool completely in tin. Drizzle with melted chocolate and scatter over additional crushed Maltesers, if you like, before cutting into squares.