Heat oven to 200C/fan 180C/gas 6. Using a sharp knife, score a line around the equator of each apple. Put them into a baking dish with a small splash of water in the bottom.
In a bowl, combine the ginger, cinnamon, prunes and sugar. Stuff the mixture into the apples so that they are well packed. Top each with a knob of butter and bake for 35-40 mins, or until cooked through. To test, pierce with a sharp knife – it should slide straight through. The apples can be cooked up to a day ahead, then warmed through in the oven or microwave before eating.
Remove from the oven and baste the apples with the liquid left in the dish. Serve hot or warm with the ice cream.