High-Fiber Apple Crumble Cake

Steps

1. Preheat the oven to 180°C (350°F). Lightly grease a 23 cm (9-inch) round or square cake pan and line the base with parchment paper.
2. Core and dice the apples into small cubes. Toss with the lemon juice in a bowl so the pieces are evenly coated, then set aside.
3. From the measured whole wheat flour, place 20 g into a small bowl for the crumble topping and keep the remaining 200 g for the batter.
4. Make the crumble: To the 20 g flour, add the rolled oats, 30 g brown sugar, and 2 g ground cinnamon. Add the cold butter and rub it in with your fingertips until the mixture forms moist, clumpy crumbs. Refrigerate the bowl while you prepare the cake batter.
5. In a large mixing bowl, whisk together the remaining 200 g whole wheat flour, baking powder, baking soda, fine sea salt, 6 g ground cinnamon, ground nutmeg, ground flaxseed, and 150 g brown sugar until well combined and no lumps of sugar remain.
6. In a separate bowl or large jug, whisk the eggs, milk, unsweetened applesauce, neutral vegetable oil, and vanilla extract until smooth and fully blended.
7. Pour the wet mixture into the dry ingredients. Stir with a spatula just until a smooth batter forms and no dry pockets of flour remain. Gently fold in the diced apples, distributing them evenly without overmixing.
8. Scrape the batter into the prepared pan and level the surface. Sprinkle the chilled crumble evenly over the top, covering the batter from edge to edge.
9. Bake at 180°C (350°F) for 35–40 minutes, until the crumble topping is deep golden brown, the edges of the cake pull slightly away from the pan, the center springs back lightly when pressed, and a toothpick inserted into the center comes out with a few moist crumbs but no wet batter.
10. Place the pan on a wire rack and let the cake rest in the pan for about 15 minutes. Run a thin knife around the edge, lift the cake out using the parchment, and set it directly on the rack. Let stand for about 30 minutes before slicing and serving.