1. Preheat the oven to 190c. Grease a 20x26cm baking dish or cake tin.

To Make the Crumble

1. Place all the crumble ingredients in a medium bowl. Using a pastry cutter or two knives, chop everything together until you have a lumpy, crumbly texture. If you like your crumble much finer, rub the mixture between your finger-tips to break up the lumps of butter. Set aside.

To Make the Cake

1. In a small bowl mix together the psyllium husks and water. If using ground flax/linseeds instead, use 1 tablespoon of seeds and 2 tablespoons of water instead.
2. In a medium bowl, combine the flour, baking powder, and fine sea salt. Whisk well to combine. Set aside.
3. In a separate medium bowl, place the vegan butter. Using a stand mixer or a hand mixer, beat the butter for a minute or until smooth and light. Add the thickened psyllium husks, sugars, vanilla, and lemon zest and beat again to combine. Note that psyllium husks like to clump together, so be sure to beat until smooth.
4. Alternating between the soy yogurt and the flour mixture, add a few spoonfuls at a time, beating to combine between each addition. Once fully combined, add the soy milk and beat for a final time. You should now have a thick cake batter.
5. Add ¾ of the blueberries and very gently fold them into the batter. Transfer the batter to the prepared baking tray or cake tin and spread smooth with the back of a spoon. Top with the remaining blueberries.
6. Finally, top the cake with the crumble topping and place in the preheated oven for 30-35 minutes or until puffed in the centre and the crumble is browned nicely.
7. Remove once baked and allow to cool fully on a wire cooling rack before slicing and serving.