Carefully use a slotted metal spoon or fish slice to place two doughnuts into the hot oil, and fry for 1-2 minutes on each side until golden brown. Lift onto the kitchen paper. Once all the doughnuts are fried, lift the doughnuts onto a wire rack. Mix the vanilla into the icing sugar with enough milk to make a thin runny icing. Add some colour, if you like, then spoon all over the doughnuts to coat.