Preheat the oven to 180°C (350°F).
Prepare the crumble topping: In a medium bowl, combine the flour, oats, and salt. Add the diced cold butter and rub it in with your fingertips until the mixture resembles coarse breadcrumbs. Stir in the brown sugar and set aside.
Prepare the apple filling: Peel, quarter, and core the apples, then cut them into thin slices. Place them in a large bowl and toss with the lemon juice, brown sugar, flour, cinnamon, ginger, and salt until well coated.
Assemble: Butter a Ø 26 cm ovenproof baking dish (or equivalent size casserole dish). Transfer the apples to the dish, scraping the bowl to include all the juices and spices. Evenly sprinkle the crumble mixture over the top without pressing it down.
Bake: Place in the middle rack of the oven and bake uncovered for 35–45 minutes, until the topping is golden brown and the apples are bubbling.
Serve: Sprinkle with powdered sugar (if using) and enjoy warm!
Tips for the Best Apple Crumble:
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