Sieve the flour and salt and add the cocoa. Mix well over a bowl of warm water; cream together the butter and sugar till light and fluffy. Beat the egg. Add egg and flour alternately to the creamed mixture, beating each well in; if necessary add a spoonful or more of milk. The mixture should be a stiff paste. Roll out on a floured board; cut in fingers one inch wide and 2 inches long. Lay these on a greased baking sheet and bake in a moderate oven for 10 minutes.
Cool and when cold put together with:
1 dessertspoon cornflour
1 oz sugar
1 oz cocoa or grated chocolate and if liked a few drops of vanilla
1/2 pint milk
1 oz unsalted butter
With a little milk mix the cornflour to a smooth paste. Set rest of the milk in a small suacepan to boil and when boiling stir in the paste. Return to saucepan and bring back to the boil for 3 minutes. Now cream togther sugar and butter and add to it cocoa or chocolate. Drop a teaspoonsful at a time of cold cornflour mixture into this and beat well with an whisk. This makes a great delicious thick chocolate cream filling.