Preheat the oven to 180C/350F/gas mark 4
Use a 15cm/6 inch cake tin.
Line and grease the cake tin. Mix the flour and salt in a mixing bowl. Rub in the butter until the mixture resembles fine breadcrumbs. Add the sugar and grated citrus rind. In a bowl, mix the sour cream with 30 ml/2 tbs. of the milk and stir into the flour mixture. Gradually add the citrus juice, beating vigorously. If necessary, add the remaining milk to give a consistency that just drops off the end of a wooden spoon.
Spoon the mixture into the cake tin and bake for 1-1 1/2 hours or until cooked through. Cool on a wire rack.
