Melt half of the chocolate in a bowl, over simmering water. Grate the other half.
When the chocolate has cooled, mix it with the custard.
Pour the coffee into a shallow dish. Dip the lady fingers, each at a time, for a few seconds. They should not become soggy. Layer these in a dish or individual glasses, then spread over third or half of the custard (depending on the depth of the dish).
Repeat the layering once or twice until you reach the edge of the glass. The custard should be the top layer.
Refrigerate for at least 2 hours.
Sprinkle with the grated chocolate before serving, then garnish with some berries.