1. Preheat the oven to 180°C and brush a deep 25cm cake tin with vegetable oil.
2. In a large bowl whisk the egg whites with an electric whisk, gradually adding in the sugar until you get stiff peaks.
3. In another bowl stir together the egg yolks, vegetable oil, bicarb, lemon juice, lemon zest, polenta/cornmeal, ground almonds and salt until well combined.
4. Add half of the egg whites to this mixture and stir in well to loosen it. Fold in the remaining egg whites gently using a rubber spatula until no streaks of egg white remain.
5. Pour the batter into the prepared tin and bake for 30 u2013 35 minutes until golden brown, and a skewer inserted into the centre of the cake comes out clean. Leave the cake in its tin for the syrup.
6. In a small pan combine all of the syrup ingredients and stir over a medium heat until the sugar has dissolved, then bring to a boil and simmer for a minute.
7. Poke holes all over the surface of the cake and pour the hot syrup over so that it soaks in evenly. Leave until fully cooled then turn the cake out onto a plate and dust with icing sugar.
8. For the rhubarb compote, combine the rhubarb, sugar and water in a small pan. Stir over a medium heat and bring to the boil, turn down to a simmer and cook, stirring occasionally, until the rhubarb has cooked down.
9. The compote can be served like this or blended for a smooth coulis.