Preheat your oven to 375 degrees Fahrenheit.
Peel, core, and slice the apples into uniform half-inch thick wedges.
Toss the apple slices with 1/2 cup sugar and cinnamon in a large mixing bowl until evenly coated.
Transfer the apple mixture into a greased baking dish and spread into an even layer.
In a separate medium bowl, whisk together the flour and the second 1/2 cup of sugar.
Cut the cold butter into the flour mixture using a pastry cutter until the texture resembles coarse, shaggy breadcrumbs.
Fold in the rolled oats until just combined.
Sprinkle the topping evenly over the apple base without packing it down.
Bake for 40 minutes until the top is deep golden brown.
Remove from the oven and let rest for 10 minutes before serving to allow the fruit juices to set.