Put the apples, butter, cinnamon, 1 tbsp sugar and the lemon juice into a pan. Cook for about 10 minutes on a medium heat, until the apples have softened slightly. Stir in the cornflour and raisins, then tip the mixture into a 25cm/10in square or round ovenproof baking dish. Top with the flapjack mix in an even layer. Bake on the middle shelf of the oven for 40–45 mins.