Push a slice of grapefruit to the base of each of 6 buttered pudding moulds or ramekins and drizzle with a tablespoon of golden syrup. Set aside.
Cream together the butter and sugar until light and fluffy. Add the eggs, one at a time, beating well until incorporated. Gently fold in the flour, salt and lime rind, then fold in the grapefruit juice and milk so that the mixture has a good dropping consistency.
Spoon the mixture into the moulds or ramekins and smooth down.
Put the moulds in a large roasting tin half-filled with boiling water and cook in a preheated oven, 180°C (350°F), Gas Mark 4, for about 40 minutes or until risen and golden.
Remove the cakes from the oven, lift them out of the hot water and leave to cool for 5 minutes. Loosen the sides of the cakes by running a knife around the inside of the moulds and then turn them out into serving bowls. Serve immediately with cream.