01 -  Peel, core, and dice the seasonal apples. Place them evenly onto a lined baking sheet. 
 02 -  In a mixing bowl, combine flour, oats, granulated sugar, and ground cinnamon. Add cold, diced butter and crumble together using your hands or a pastry cutter until the mixture resembles coarse crumbs. 
 03 -  Sprinkle the crumble mixture evenly over the diced apples on the baking sheet. Bake in a preheated oven at 180°C (350°F) for 30-35 minutes, or until the top is golden and crispy. 
 04 -  Allow the apple crumble bars to cool for 10-15 minutes before cutting into squares. Serve warm or at room temperature.