Preheat the oven to 180C/350F/gas mark 4
Use a deep 20cm/8 inch square cake tin.
Combine dates, water and soda in bowl, cover, stand overnight. Grease and line the base of the cake tin with paper. Grease the paper well.
Cream the butter and sugar in a small bowl until light and fluffy. Add sour cream and mix well. Transfer mixture to large bowl, stir in half the sifted flours and half the undrained date mixture, then stir in remaining flours and date mixture. Spread into the prepared tin. Bake for about 1 1/4 hours. Stand 5 minutes before turning on to wire rack to cool.
