Sit a heatproof bowl over a pan of barely simmering water, but don't let the bowl touch the water. Then place the eggs, sugar, lemon zest and juice in the bowl and whisk together. Now add the butter ...
To make the lemon curd, place the egg yolks, granulated sugar, butter, lemon zest and lemon juice in a glass bowl over a saucepan of simmering water (don’t let the bowl touch the water).
Cut the zested lemon in half and squeeze the juice. Set it aside to make the icing. For the cake, place the two whole (or one large) lemons in a small saucepan, cover with water, bring to the boil ...