Preheat oven to 180°C.
Boil 1 cup water in a deep non-stick pan and add chocolate. Mix well and switch off heat. Set aside to cool.
Break eggs into a bowl and beat well with an electric beater till light and frothy.Add sugar free and beat again till well mixed.
Sift together refined flour, salt and baking soda into the bowl. Mix well, add chocolate and mix again. Add buttermilk and mix again.
Add walnuts and oil and mix again. Add citric acid and mix. Pour into a baking dish, place it in the preheated oven and bake for 30-40 minutes.
Remove from oven, cool, slice and serve.