Preheat the oven to 180°C (350°F). Grease or line an 8-inch (20 cm) springform or loose-bottom cake pan with parchment paper.

Add all the dry ingredients to a large mixing bowl and mix until everything is well combined.

Add all of the wet ingredients to the bowl and mix until just combined. The batter should be thick. Scoop or pour the batter into the cake pan and smooth the top with a spoon or spatula.

Using the same bowl (or a smaller clean bowl), add all the ingredients for the topping. Mix with a spoon or your fingertips until combined. There shouldn't be any chunks of butter or flour.

Arrange the thinly sliced apple on the top of the cake in 'fan' shapes or as desired. Sprinkle the crumble in the gaps on top of the cake.

Bake the cake for 55-60 minutes. If the crumble topping is browning too quickly, tent the cake pan with aluminum foil or cover the pan with an oven-safe plate. The cake is ready when you can insert a toothpick in the middle and there is no wet batter on it. The cake is very moist so a few crumbs on the toothpick are fine.

Rest the cake in the cake pan for 10-15 minutes. Remove the cake from the pan and allow it cool entirely on a cooling rack.

If desired, dust the cake with powdered sugar or drizzle with a simple glaze (note 4). Enjoy with dairy-free yogurt, vegan ice cream or/and a cup of coffee.

Store leftovers in an airtight container at room temperature for 1 day, in the fridge for 3 days or in the freezer for up to 1 month.