Preheat the oven to 180C/350F/gas mark 4
Use a 20cm/8 inch ring tin.
Grease and lightly flour the ring tin, shaking out excess flour. Cream the butter, rind and sugar in small bowl with until light and fluffy. Whisk in sour cream, beat until combined. Transfer mixture to large bowl, stir in half the flour, the baking powder and half the buttermilk, then stir in remaining flour and buttermilk.
Spread the mixture into the prepared tin. Bake for about 1 hour. Stand for five minutes before turning out on a wire rack. Pour hot lime syrup evenly over the cake.
Lime Syrup: Combine lime juice, sugar and water in saucepan. Stir over the heat until the sugar dissolves. Bring to the boil; remove from heat.
