Preheat the oven to 160⁰C (fan). Grease and line the bottom of two 8-inch deep, round cake tins.
In a stand mixer, beat together the vegetable oil, yoghurt, eggs, sugar, lemon zest and buttermilk until combined. Add the flour, baking powder, bicarbonate of soda and salt, and mix until just combined.
Divide the batter equally between the two cake tins and bake on the middle shelf for 30 – 35 minutes, until a skewer comes out clean when inserted into the centre.
Remove and allow to cool for 10 minutes, before removing from cake tins and leaving to cool completely on a wire rack.
While the cakes, it's time to make your compote. Add the blackberries, honey, lavender and lemon juice to a small pan. Stirring occasionally, bring the mixture to the boil, then reduce the heat and smash the berries with a potato masher or the back of a fork.
Allow the mixture to simmer until reduced by half, stirring to ensure the seeds do not stick to the bottom of the pan. Allow to cool.
While the cakes are cooling, make the buttercream. Break the chocolate into a bowl and place over a pan of barely simmering water (not allowing the water to touch the bottom of the bowl) and melt the chocolate gently.
Once just melted, remove from the heat and allow to cool. In a stand mixer, add the butter and icing sugar and beat until smooth and light. Add the cooled, melted chocolate and gently beat to combine.
6. Once all three elements are cool, assemble the cake. Using a large serrated knife, or cake slicer, divide each cake in two. Place one layer on a serving plate and spread a fifth of the buttercream on top, followed by a thin layer of the compote. Continue to do this until the last layer is in place.
Use the remainder of the buttercream to cover the top of the cake and lightly cover the sides. Chill for 30 minutes and serve. Alternatively, keep the cake in the fridge for a day.
If you try this recipe for yourself, be sure to share your photos with us over on our social media platforms. We'll be getting in The Great British Bake Off spirit over the next few months, so watch this space for more baking inspiration.