Prepare for the baking: Line the bottom of a 2LB loaf tin with baking paper. Preheat the oven to 175°C/350°F/Gas Mark 4.
Make the flax “egg”: Starting by mix the ground flaxseed and aquafaba in a small bowl. Stir and let it sit while we mix other ingredients.
Mix dry ingredients: Add flour, rolled oats, sugar, and salt into a big mixing bowl. Use a fork or spoon to mix them together evenly.
Add wet ingredients: Add coconut oil, vanilla extract, and the flax “egg” to the dry ingredients. Mix to combine. The mixture should come together.
Shaping: Transfer about 2/3 the mixture to the lined loaf tin. Use a silicone spatula to press the mixture down evenly into a single layer. Set it aside for later.
Make the chocolate filling:
Melt the chocolate: Add the chopped chocolate to a heat-resistant bowl or a big measuring jug. Melt the chocolate by microwaving for 40 – 60 seconds or using a double boiler. Stir to make sure the chocolate is fully melted.
Add other wet ingredients: To the melted chocolate, add aquafaba, nut butter, vanilla extract, and salt. Stir to combine all.
Add the dry ingredients: Add the flour and sugar. Stir again to combine until everything is incorporated.
Assemble:
Add chocoolate filling: Transfer the chocolate filling mixture on to the base. Spread it out evenly to cover the base.
Add the crumble topping: Sprinkle the saved crumble mixture on top of the chocolate layer evenly. Use a spatula to gently press them down, so they can stick to the chocolate layers.
Bake: Place the loaf tin in the oven on a lower ⅓ rack to bake at 175°C/350°F/Gas Mark 4 for 25–30 minutes until the topping is slightly golden brown.
Cool: Transfer the loaf tin onto a wire rack to cool down for 20 minutes. Then remove the block from the loaf tin to cool down completely.
Cut: Use a sharp knife to cut it into 8 squares. Enjoy!