Peel the apples and cut vertically to remove core and seeds. Heat half the butter in a heavy based frying pan and toss in the apples. Sprinkle with icing sugar and cook for 5 minutes over a high heat until caramelised. Remove from the heat and keep warm. Pour the beaten eggs into a shallow dish. Heat the remaining butter with 1 tbsp. sunflower oil until the butter stops foaming. Dip the brioche in the beaten egg on both sides and add the pan. Cook over a medium heat until golden brown, turn and cook the other side. Once cooked, place the brioche slices on warm plates and top with the apples. Add a scoop of mascarpone, dust with icing sugar and serve.