Break up the chocolate brownies and arrange them at the base of 10 individual glass dishes. Drizzle over the chocolate liqueur.
Melt the chocolate in a bowl over a pan of simmering water (see
Mix the egg yolks, sugar and cornflour for the custard in a jug. Bring the cream to the boil in a pan, then pour it over the egg mixture, whisking all the time. Return the custard to the pan and heat gently, stirring all the time, until the sauce is thickened and smooth. Pour the custard into a jug and cover with nonstick baking paper. Chill for 1 hour. Once the chocolate layer has set, pour the custard over and chill.
Whip the cream until softly peaking, then fold in the vanilla extract and maple syrup. Spoon the cream on top of the custard. Decorate with the chocolate thins.