Preheat the oven to 160C/325F/gas mark 3
Use an 18cm/7 inch square cake tin.
Grease and line the cake tin with greased greaseproof. Using the all-in-one method, measure the flour, spice, soft butter, caster sugar, black treacle, sour cream and sultanas into one bowl and mix until all the ingredients are well blended. Turn the mixture into the prepared tin and level out the top. Bake in the oven for about 1 - 1 1/4 hours until a warm knife comes out clean when pushed into the centre of the cake. Turn on to a cooling tray. To serve, dust the top with sieved icing sugar.
