1. Preheat your oven to 350°F (175°C). Grease a 9-inch square baking dish with a little butter or line it with parchment paper for easy cleanup.
2. In a large mixing bowl, toss the sliced apples with granulated sugar, cinnamon, nutmeg, and lemon juice. This helps the apples release a little juice and infuses them with warmth and brightness. Set aside to marinate while you prepare the topping.
3. In another bowl, combine rolled oats, all-purpose flour, brown sugar, and sea salt. Using your fingertips or a pastry cutter, rub the cold cubed butter into the dry ingredients until the mixture resembles coarse crumbs. If you’re adding nuts, fold them in now for that lovely crunch.
4. Pour the apple mixture into your prepared baking dish, spreading it out evenly. Sprinkle the oat topping generously over the apples, covering them completely but without pressing down too firmly—this keeps the topping light and crisp.
5. Bake in the preheated oven for 40 to 45 minutes, or until the topping is golden brown and the apple juices are bubbling up around the edges. You’ll know it’s done when the aroma fills the kitchen and the topping has a satisfying crunch when tapped.
6. Remove from the oven and let the apple crisp cool for at least 15 minutes before serving. This helps the juices thicken slightly, making every spoonful a perfect balance of gooey and crisp—just like my mum’s used to be.

One little secret I picked up from those early mornings in the cottage kitchen: if you want to take the topping to the next level, try sprinkling a tiny pinch of flaky sea salt on top just before baking. It cuts through the sweetness beautifully and adds a subtle complexity.