Mix the bicarb with the milk. Add to the butter mixture. Beat eggs and add, & stir in raisins if you wish to.
Sift the flour, salt, ginger and nutmeg together. Add the butter mixture and stir till smooth.
Place the mixture in a deep ovenproof dish.
Mix the remaining ingredients (water, sugar and vinegar) in a saucepan over medium heat until the sugar is dissolved. Pour 1/2 the sauce slowly over the cake mixture.
Bake at 180C degrees for 45 minutes. Add the rest of the sauce 20 minutes times into the baking process. There is a lot of sauce and the cake will absorb it. Test with a skewer if it is baked through. Serve with custard.