Dissolve soda in warm milk and put aside while you Cream the butter Butter and sugar. then add the soda/milk and warmed syrup and beat well.
Combine the flour, ginger, cinnamon, cocoa and salt in a bowl and add the creamed mixture. you may need to add more flour to get to the right consistancy and don't be affraid to get your hands in there either :P
Roll into small balls and place on a tray lined with grese proof paper then press down with a fork. bake fo about 20 minutes at 180degC/350degF, depending on how crunchy you want them.
When done take out and let cool, then enjoy :)