Use a 23cm flan dish or non-metallic pie plate. Peel the pumpkin and cut into chunks; discard seeds. Place in a saucepan with the orange juice. Bring to the boil, then lower the heat and cook gently, covered, for 20–25 minutes or until tender. Drain, discarding the remaining juice. Purée finely in a food processor or mash well. Preheat oven to 180 degrees C.
Beat the eggs with the orange rind, sugar, cinnamon, ginger, nutmeg, salt, brandy, if using, and the sour cream. Add the pumpkin and mix well.
Bake for 25–30 minutes or until just set. Loosen the edges with a round-bladed knife, then leave to cool for 1 hour. Serve slightly warm. Alternatively, cover and chill before serving. Dust flan lightly with icing sugar and serve with sour cream.