Preheat the oven to 160 degrees C. Grease and flour a heart shaped cake tin.
Beat egg yolks and sugar together using an electric beater until light and frothy then add vegetable oil, lemon juice, vanilla extract and water. Continue to beat until smooth.
Add flour and baking powder then continue to beat until you obtain a smooth, frothy mixture.
Wash and dry the electric beaters. Then use them to beat the egg whites with one or two pinches of bicarbonate of soda, until soft peaks form. Fold egg white mixture into the cake batter.
Pour the cake mixture into the tin. Place a smaller heart shaped cookie cutter in the centre of the uncooked cake, pressing it down slightly to ensure it stays in the middle during cooking.
Bake in the preheated oven for 40 minutes, or until a skewer inserted into the centre of the cake comes out clean. Remove cake from oven then cool at room temperature.
Transfer onto a serving plate then use a knife to carefully remove the heart shaped cookie cutter (and cake inside it) from the middle of the cake.
Chocolate Chips: Add some mini chocolate chips in the hollow space. You'll get a chocolaty heart within a vanilla heart shaped cake.
Red Glaze: Make a glaze by mixing icing sugar with 2 tablespoons of water. Add a few drops of red food colouring and mix well. Transfer to a pastry bag fitted with a small tip and pipe red glaze into the hollow heart space. You can write a message with remaining glaze if you like.
Covered with Glaze: Double the ingredients for the glaze and cover the entire cake in red glaze. Decorate with a ribbon.