Preheat the oven to 180°C/160C Fan/350°F. Lightly grease two 8-inch round cake pans and line with baking paper. Sieve the flour and baking podwer together into a medium bowl, add the lemon zest and set aside. In the bowl of an electric stand mixer fitted with the paddle attachment, beat the butter and sugar together until light and fluffy, about 5 minutes. Add the eggs one at a time beating until fully combined. Add the flour mixture and mix until combined.
Divide the cake batter evenly between the two prepared cake pans and gently level out. Bake in the preheated oven for 25 minutes. The cake should be golden brown and be coming away from the edge of the tin. Test with a cocktail stick to ensure the cake is thoroughly cooked.
Cool in their tins for ten minutes before turning out and cooling completely on a wire rack.
To make the lemon curd put the lemon juice and zest in a saucepan and bring to the boil.
In a mixing bowl whisk together the eggs and sugar until light in colour. Add half the lemon juice to the egg mixture and whisk until fully mixed.
Add the mixture back to the saucepan with the remaining lemon juice and cook over a low heat for 5 mins or until thickened.
Take the pan off the heat and pass the mixture through a sieve, then stir through the butter piece by piece until fully melted and incorporated.
Pour into a dish and cover with cling-film, making sure to press it down onto the surface of the lemon curd. Leave to cool.
To assemble spread one layer of cake with the lemon curd (you will not use all of the curd, so just use however much you want) and top with the whipped cream. Sandwich together with the second layer of cake and sprinkle with a dusting of icing sugar.