Preheat the oven to 180°C. Lightly grease a 23cm x 23cm/9x9in square pan with a little bit of vegan butter, then line with a strip of parchment paper. Set aside.
First, prepare cinnamon sugar swirl by combining 25 g brown cane sugar, 1 tsp ground cinnamon, and 5 g all-purpose flour in a small bowl. Set aside. For the crumble, mix 55 g brown cane sugar, 1 tsp ground cinnamon, 70 g all-purpose flour, and a pinch of salt in a medium-size bowl. Cut 50 g cold vegan butter into little pieces or grate it on a grater and add to the mixture. Use a fork to combine the ingredients until it starts to clump **.
In a large bowl, beat together with a hand mixer or whisk 95 g white cane sugar, 30g sunflower oil, and 200 g coconut sour cream (or coconut yogurt) for about 1 minute. Add 2 tbsp maple syrup, 1 tbsp apple cider vinegar, 2 tbsp unsweetened almond milk, and 1 tsp vanilla extract and mix again until combined.
In a separate bowl, combine 180 g all-purpose flour, 1 tsp baking soda, 1 tsp baking powder, and ¼ tsp sea salt.
Sift the flour mixture into the large bowl with the wet ingredients and use a spatula or whisk to mix the batter until just combined. Don’t overmix the batter.
Pour about 300 g of the batter into the prepared pan and spread to the sides.
Next, sprinkle the cinnamon-sugar mixture over the first layer.
Pour the remaining batter into the pan and carefully spread it to the sides.
Sprinkle the crumb all over the top of the cake.
Bake in preheated oven for 30 minutes until a toothpick inserted into the middle comes out clean, and the crumb is golden brown. Otherwise, bake for 2-5 minutes longer.
Cool completely before serving. Dust the top of the cake with powder sugar.