Cake: Preheat the oven to 180 degrees C. Grease a deep 18cm cake tin and sprinkle the base and sides with flour.
Using a handheld mixer, whisk the eggs with the lemon zest and a pinch of salt.
When the eggs are starting to become firm, but are not making peaks yet, sprinkle the lavender infused sugar on top a little at a time. Keep whisking until you have a light and frothy mixture. All in all, the whisking should take you at least 10 minutes.
Working by hand, delicately add the oil and the yoghurt to the egg mixture, folding from the bottom to the top.
In a separate bowl, mix the flour and the baking powder. Still working by hand, gently fold the flour mix into egg mixture.
With a food processor, blend the blackberries. Add half of the blend to the mixture. Pour the mixture into the prepared cake tin.
Bake in the preheated oven for about 45 minutes, or until a skewer inserted into the centre comes out clean. Once the cake is ready, leave it on a wire rack to cool down.
Filling: Mix two tablespoons of blackberry jam, two tablespoons of dairy free soya yogurt and the remaining half of the blackberry blend.
To Assemble: Cut the cake in half horizontally.
Spread half the blackberry filling on the bottom half of the cake. Place the remaining blackberries on top and cover with the rest of the blackberry filling.
Cover with the upper half of the cake and dust with icing sugar.
Cake flour has a lower protein content than ordinary plain flour. It also makes lighter and fluffier baked items. If this is unavailable, you can use the following substitution: for every 100g plain flour, add 2 tablespoons cornflour.
If you do not have sunflower oil you can substitute with any other flavourless vegetable oil.