Peel, core, and dice the apples into small, even pieces, then set aside.
In a skillet over medium heat, melt a tablespoon of butter. Add the diced apples and cook for about 3-4 minutes until they soften slightly and release a fragrant aroma. Stir in lemon juice and a pinch of cinnamon, then remove from heat.
In a mixing bowl, combine oats, flour, brown sugar, cinnamon, and salt. Mix well to distribute evenly.
Add cold butter pieces to the dry mixture. Using a pastry cutter or forks, cut in the butter until the mixture resembles coarse crumbs with some pea-sized bits. Reserve about one-third of this crumble for topping.
Press half of the crumble mixture evenly into the bottom of a greased 9-inch square baking pan. This forms the crust.
Spread the cooked apple filling evenly over the crust layer.
Sprinkle the remaining crumble mixture over the apples, gently pressing down to help it stick.
Bake in a preheated oven at 180°C (350°F) for 25-30 minutes, until the crumble topping turns golden brown and the filling bubbles around the edges.
Remove from the oven and allow the bars to cool completely in the pan for at least 15 minutes. This helps them set and makes slicing easier.
Use a sharp serrated knife to cut into squares or rectangles. Serve warm or at room temperature, optionally with whipped cream or caramel drizzles.
Enjoy the fragrant aroma of baked apples and cinnamon, with a crisp topping and juicy filling in every bite!
