Roll the pastry out on a lightly floured surface until large enough to line a buttered metal pie dish, 20 cm (8 inches) in diameter and 5 cm (2 inches) deep. Lift the pastry over a rolling pin, drape into the tin then press over the base and sides. Trim the edges, then chill for 15 minutes.
Put the sweet potato in the top of a steamer, cover and cook for 10 minutes or until tender. Mash with the cream, sugar, honey and spices, then beat in the whole egg and egg yolks. Pour into the pie case, level the surface, then bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 40 minutes until set.
Make the topping. Whisk the egg whites until you have stiff peaks, then gradually whisk in the sugars, a teaspoonful at a time, until all the sugar has been added. Add the ginger and whisk for a minute or two more until very thick and glossy. Spoon over the hot pie and swirl the meringue with the back of a spoon. Bake for 15 minutes until lightly browned and the meringue is crisp.
Leave to cool for 30 minutes, then cut into wedges and serve warm with scoops of vanilla ice cream.