For the syrup: zest and juice the lemon. Place the zest and juice in a pan with the water and the sugar and bring to the boil. Simmer for 5 minutes then pass the liquid through a fine sieve and set aside.
For the sponge biscuit: preheat the oven to 180°C.
Place the butter in a saucepan and melt. Cut the vanilla pod in half and scrape out the seeds.
Beat together the yogurt and the sugar. Add the melted butter, ground almonds, vanilla seeds, orange flower water and the egg. Mix well.
In another bowl, mix together the semolina and the baking powder. Add this mixture to the orange flower water mix. Transfer into a rectangular non-stick baking dish and bake for 35 minutes.
Remove from the oven and pour the syrup over the top. Allow to cool then cut into rectangular pieces.
Peel the grapefruits, making sure to remove all of the white pith. Cut along either side of the membranes to remove the individual segments.
For the dressing: zest the lime. Place the water in a saucepan and heat gently. Add the sugar and dissolve in the water. Add the olive oil, lime zest and the fresh thyme leaves.
Place a piece of sponge biscuit on each plate and top with grapefruit segments. Drizzle the dressing over the top to serve.
«Try cooking these sponge bases in individual round moulds. Make sure to reduce the cooking time to suit the size of your moulds.»