To Make the Cake

1. Preheat the oven to 180c/355f fan. Grease and line a 32x24cm sheet pan or roasting tray.
2. In a small bowl whisk together the ground psyllium husks/ground flax seeds with the water. Set aside to thicken into your “egg” mixture.
3. Using a box grater, grate the courgettes/ zucchini into a medium bowl then transfer to a nut milk bag or piece of muslin/cheesecloth. Over the bowl, squeeze out as much moisture as you can from the courgettes/ zucchinis. You can reserve the liquid to use in smoothies and juices if you like. Set aside the grated, drained courgettes/ zucchinis.
4. In a medium bowl mix together, the flour, baking powder, baking soda, and salt. Set aside.
5. In the cup of a high-speed blender or food processor, add the plant milk, lemon juice, vanilla, vegetable oil, and thickened psyllium husks. Blend on high speed for 30 seconds. If you don’t have a food processor, use an immersion blender. The blended mixture should be thick, smooth, and creamy, almost like mayo. Set aside.
6. In a large bowl or the bowl of a stand mixer fitted with the paddle attachment, place the caster sugar and lemon zest. Add the plant milk/vegetable oil mixture and beat well until the mixture is smooth and glossy.
7. Add the flour mixture in three additions, mixing gently between each addition. Do not over-work the batter. Finally, add the grated courgettes/ zucchini and mix to combine. Pour the batter into the prepared tin and place in the preheated oven. Bake for 40 minutes, rotating the sheet-tin halfway through.
8. Once baked, remove from the oven and place the baking tray on a wire cooling rack. Allow the cake to cool completely.

To Make the Frosting

1. Once the cake is room temperature, sieve the icing sugar into a medium bowl and set aside.
2. If using a vegan butter which browns (see note below) place half of the vegan butter (55g) into a medium saucepan and place over medium heat. Allow melting, stirring constantly, until it foams. The foam should subside and the vegan butter will begin to be dotted with small dark flecks. Don’t allow the butter to burn, just brown. Remove from the heat and pour it into a medium bowl. Allow cooling for 10 minutes.
3. If you don’t have access to vegan butter which browns, add a tsp of vanilla extract at this stage.
4. Once the browned butter is cooled slightly pour it into a large bowl or the bowl of a stand mixer fitted with the whisk attachment. Add the other half of the vegan butter and whisk together until completely smooth.
5. Add the icing sugar in four additions, whisking well to ensure the frosting is smooth. Once all the icing sugar is added, frost the now completely cooled cake. Once frosted, top with a few toasted hazelnuts, just to add some more nuttiness to the cake.
6. Slice the cake into pieces and serve.