method
1. Heat the oven to 160°C (325°F).
2. Combine the flour, cornstarch and cocoa powder with a little of the milk to make a paste.
3. Put the rest of the milk in a saucepan with the coffee and 4 tablespoons of the sugar. Heat, stirring, to dissolve the sugar.
4. Stir a little of this hot liquid into the chocolate paste, then add this to the remaining liquid in the pan.
5. Bring to the boil, stirring until thickened. Pour the custard into a baking dish.
6. Rub together the butter, graham crackers, oats and remaining sugar and scatter over the coffee custard.
7. Bake for 20 minutes. Serve hot or cold.
