Cut the plums into quarters discarding the stones and place them in a pan with the port and sugar. Cook them on a low heat for approx. 7 minutes until slightly softened. In the meantime grease an oven-proof dish (2 litres) and place the plums into it.
In large bowl, sieve both flours and mix in the sugar. Using your finger tips, rub in the butter creating a fine and crumbly mixture. In a separate bowl mix together the egg and the milk until smooth and then stir into the flour. Place large spoonfuls of topping onto the plums and bake in the middle of a pre-heated oven of 180C for approx. 35 minutes or until the top is cooked through.
Before serving dust with a lot of icing sugar.