Wine Sauce: In a small bowl, mix together cornflour, egg yolks and just enough milk to make a smooth paste.
Bring the scraped vanilla bean, sugar and remaining milk to the boil. Whisk in the cornflour mixture and wine. Bring to the boil. Remove from heat and beat a few times. Let cool.
Filling: Mix together hazelnuts, sugar, sultanas, butter and cinnamon. Use to stuff the apple cavities.
Transfer apples to a buttered ovenproof dish. Pour over wine sauce and bake uncovered for 30-40 minutes. Serve with ice cold vanilla custard.