1. Place the whole lemon into a large deep saucepan, cover with cold water and a small heatproof plate (to keep the lemon submerged). Place the pan on a medium heat, bring to a simmer and cook for 20 minutes, or until the lemon is soft (you might need to top up with more water, if the water evaporates too much).
2. Drain the lemon and set aside to cool completely, then cut it into quarters
removing any pips. Place the lemon quarters into a blender or food processor, then blitz with the extra virgin olive oil until smooth.
3. Preheat the oven to 160’c. Grease and line a deep 20cm cake tin.
4. Whisk the eggs and sugar together in a large bowl, then whisk in the lemon and oil purée, the ground almonds and polenta. Pour the mixture into the prepared tin, spread out evenly with a palette knife and bake for 40 to 45
minutes, or until risen and golden and a skewer inserted into the middle comes out clean. Leave to cool in the tin, then turn out onto a wire rack and leave to cool completely.
5. Meanwhile, make the syrup: place the salt caramel in a small pan on a medium-low heat and squeeze in the lemon juice. Bring to a simmer and cook, stirring, for 4 to 5 minutes, until the syrup has melted (you may need to add a splash of hot water if it looks too thick). Remove from the heat.
6. To make the mascarpone cream, beat the mascarpone, icing sugar and vanilla paste together, then gently fold in the yoghurt and set aside.
7. Tip the almonds into a small, dry frying pan and toast until golden. Keep an eye on them!
8. To assemble the cake, place the sponge in the middle of the plate. Spoon the mascarpone cream on top making peaks and waves, then drizzle over the syrup and garnish with the toasted almonds.