Line 2 baking pans with baking paper or grease them with butter. I used 2 18cm diameter pans and had 4 layers of sponge in the end, but you can use bigger pans too, the only difference being that you won't get as many layers as I did.
Mix the buttermilk with lemon juice and baking soda.
Mix the flour with coconut, salt and baking powder.
Mix the butter, oil, sugar and vanilla in a bowl until creamy and double in volume. Stir in the lemon zest then add the eggs, one by one.
Stir in the sour cream.
Begin folding in the flour and buttermilk, alternating them. Always start and end with flour.
Divide the batter between the two prepared pans and bake in for 50 up to 60 minutes. Check the cakes with a toothpick.
Whip the heavy cream with powdered sugar until stiff. Add more sugar if you like it sweeter.
Stir in the vanilla extract.
Pour one cup of water in a small saucepan and bring it to a boil over medium flame.
To make the curd, prepare a heatproof bowl that fits the saucepan but its bottom doesn't touch the boiling water.
Combine all the ingredients into the bowl and mix roughly.
Place the bowl over the boiling water and cook for 20-25 minutes, mixing often.
It is a slow process, but the final curd is well worth the result.
Cook until the mixture begins to thicken then remove from heat and strain through a fine sieve.
Let it cool in the fridge before using.
2 18cm diameter cake pans
To fill the cake, see the picture below. One layer of whipped cream and one layer of lemon curd will yield a beautiful pattern and also a balanced taste.