Grease an ovenproof dish and spread the brioche with the butter. Peel and core the apples and slice. Scatter the apples and raisins over the bottom of the dish, then arrange the brioche in overlapping layers over the top. Whisk together the floc, eggs and milk, and pour over the brioche, making sure that all the slices are coated. Using a palette knife, push the brioche down to enable the egg mixture to soak in. Sprinkle the sugar over the top and place in the fridge for at least an hour (or overnight).