1/4 cup cocoa powder, plus extra, for dusting
1 1/4 cup caster sugar
1 1/4 Tbsp cornflour
2 free-range egg yolks
2 tsp vanilla extract
100g dark chocolate (70% cocoa), finely chopped
125g crunchy peanut butter
8 peanut biscuits, crumbled
In a medium bowl, mix 1/4 cup of the milk with cocoa, caster sugar, cornflour, yolks and vanilla, whisking until very smooth. Pour remaining milk into a medium saucepan and bring to a simmer over medium heat.
Pour half of the hot milk onto cocoa mixture, stirring well, then add cocoa mixture to remaining hot milk in pan and cook, stirring constantly, until mixture bubbles. Remove from heat. Beat in chocolate.
Pour hot custard into four 375ml capacity glasses. Heat peanut butter gently in a small saucepan over low heat until just runny, then marble into custard. Allow to set, top with biscuits and dust with cocoa to serve.