Preheat the oven to 180°C/350°F/Gas Mark 4. Mix together the condensed milk and one and half tablespoons butter and heat it gently for two to three minutes. Set aside to cool. Mix in half the cinnamon powder.
Peel and slice the apples. Take a six-inch diameter oven proof dish and place the apple slices in layers. Press lightly while placing them. Pour the condensed milk mixture over the apples and spread it evenly.
Mix the refined flour, the remaining butter and the remaining cinnamon powder with your finger tips till it resembles breadcrumbs. Sprinkle generously on the apples, so as to cover them completely.
Bake in the preheated oven for forty five minutes or till the crumble topping turns golden brown. Serve hot or warm.