Grease two 20cm round sandwich tins and line the bases of the cake tin with baking parchment. Preheat the oven to 180°C / 350°F / Gas Mark 4.
Steam the spinach on the stove until it is unfrozen (if using frozen) or wilted (if using fresh).
Give the spinach a good squeeze to remove excess water, then whizz it up in your blended until smooth.
Whisk the oil, aquafaba, and sugar until the mixture is well combined, lighter, and noticeably thickened.
Fold the blended spinach into the aquafaba & sugar mixture until it is completely mixed.
Gently fold in the flour & baking powder & mix until combined.
Evenly divide the mixture into the two tins.
Pop in the oven and bake for 35-40 mins. Test with a skewer to see if it is cooked through. If it comes out clean, it's ready to take out of the oven. If it comes out a little gooey, leave the cake in for another 5 mins.
Cool the cake in it's tin for 10 mins, then turn out onto a cake rack.
For the Buttercream
Using a whisk, whizz up the vegan butter/margarine, sugar and lemon oil until it is floofy (technical term)
Sandwich the cake together with the buttercream. Add fresh berried if you would like! Top with more buttercream & extra berries.