FOR THE BROWNIE SANDWICHES
1 Preheat the oven to 190 degrees (175 degrees fan). Grease and line a 40cm x 30cm baking tray with parchment paper.

2 Put the butter, chocolate and salt in a heat-proof bowl over a pan of simmering water and melt gently. Alternatively, melt the chocolate in the microwave in 30-second bursts. Once melted, set aside to cool slightly.

3 Meanwhile, whisk the egg whites and sugar together to a soft peak.

4 Whisk the egg yolks into the cooled chocolate and butter mixture, and gently fold in the whisked egg whites in thirds, taking care not to over-mix.

5 Sift in the cocoa powder, and fold through gently. Spread the brownie mix on to the prepared baking tray and bake in the preheated oven for 12 minutes, until cooked through and firm to the touch.

6 Remove from the oven and cool completely before slicing in half lengthways into two long strips. Store in the fridge until ready to assemble the sandwiches.

FOR THE ICE-CREAM
1 Put the milk, cream, mint leaves and mint extract into a large saucepan and bring to a simmer. Turn off the heat and allow to infuse for 15 minutes. Remove the mint leaves and bring back to a boil.

2 In a bowl, whisk the egg yolks and sugar together. Pour the hot milk mix over the egg yolks, whisking all the time. Pour the mix back in to a clean pan and cook over a low heat, stirring constantly for about 10 minutes until thickened and coating the back of a spoon. Transfer to a clean bowl and cool completely. Add the chopped chocolate once the mix is cold.

3 If using an ice-cream machine, pour in the custard and churn until thick, frozen and smooth. If working by hand, freeze the custard in a container, whisking well every hour for about three to four hours, until just set, but spreadable.

4 Smooth the set ice-cream on to one of the brownie strips and place the second strip on top. Freeze for at least an hour before slicing into 10 bars.