The "Irishness" of this lovely chocolate cake is thanks not only to the wonderful liqueur used in the filling, but also to a certain, very Irish, ingredient in the cake mixture itself, which contributes to its moistness.

Preheat oven to gas mark 5/ 190°C/ 375°F, and grease and line two 20cm/ 8 inch cake tins. Sift flour and salt into a mixing bowl. Melt chocolate in a bowl placed over a saucepan of hot water. In a separate bowl, cream butter and sugar together until fluffy, then beat in the chocolate and mashed potato. Gradually beat in the eggs, adding a little flour with each addition. Fold in the rest of the flour and stir in the milk.

Divide mixture between cake tins and bake for 25-30 minutes or until top is firm but springy to the touch. Remove from oven and after a few minutes, turn out on a cooling rack. While the cake is cooling, make the filling. Melt the chocolate as before, stir in the other ingredients and mix well. Use the filling to sandwich the sponge layers together and coat the top and sides of the cake.