For the Cake:

• Preheat the Oven: Preheat your oven to 180°C (160°C fan) or 350°F. Grease and line two 20cm (8-inch) round cake tins with parchment paper.
• Cream the Butter and Sugar: In a large mixing bowl, use an electric mixer to cream the softened butter and caster sugar together until light and fluffy.
• Add the Eggs: Add the eggs one at a time, beating well after each addition. Mix in the lemon zest and juice.
• Sift in the Dry Ingredients: Sift the self-raising flour and baking powder into the mixture. Fold gently until just combined, taking care not to overmix.
• Bake the Cakes: Divide the batter evenly between the prepared cake tins. Bake in the preheated oven for 25-30 minutes, or until a skewer inserted into the center of the cakes comes out clean.
• Cool the Cakes: Allow the cakes to cool in the tins for 10 minutes before turning them out onto a cooling rack to cool completely.

For the Lemon Curd:

• Prepare the Ingredients: Zest and juice the lemons, ensuring you have about 125ml of lemon juice. Set the zest and juice aside.
• Combine Ingredients: In a heatproof bowl, whisk together the eggs, egg yolk, and caster sugar until well combined. Add the lemon juice, zest, and butter cubes to the mixture.
• Cook the Lemon Curd: Place the bowl over a saucepan of gently simmering water, making sure the bottom of the bowl doesn’t touch the water. Stir continuously with a whisk until the butter melts and the mixture thickens. This process usually takes about 10-15 minutes. The lemon curd is ready when it coats the back of a spoon and holds its shape.
• Strain the Curd: For a smooth finish, strain the lemon curd through a fine sieve into a clean bowl to remove the zest and any bits of cooked egg. Allow the curd to cool before using.

For the Assembly:

• Fill the Cake: Once the cakes are completely cool, spread a generous layer of lemon curd on top of one of the cakes. Place the second cake on top to sandwich the curd between the layers.
• Top with Lemon Curd: Spread a layer of lemon curd on top of the cake. You can also spread some around the sides if you prefer.
• Dust with Icing Sugar: Just before serving, dust the top of the cake with a light layer of icing sugar for a finishing touch.