Preheat oven 375 degrees F. Grease and line 2 (8") cake pans. Sift flour and salt into a mixing bowl. Melt 2 oz of dark 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 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 remaining dark chocolate as before, stir in the heavy cream, sugar and Irish Cream liqueur and mix well.

 

Use the filling to sandwich the sponge layers together and coat the top and sides of the cake.