Preheat oven to 180 C / Gas 4. Grease and flour two 20cm round cake tins. Mix together the flour, baking powder and salt. Set aside.
In a large bowl, cream together the butter and sugar until light and fluffy, about 5 minutes. Beat in the eggs one at a time, then stir in the vanilla. Beat in the flour mixture alternately with the milk, mixing just until incorporated.
Pour mixture into prepared tins. Bake for 30 minutes, or until a skewer inserted into the centre of the cake comes out clean. Allow to cool in the tins on a cooling rack for 10 minutes. Then turn out to cool completely.
To make filling: In medium saucepan, mix together 1 tablespoon lemon zest, 120ml lemon juice and 1 tablespoon cornflour until smooth. Mix in 85g butter and 3150g caster sugar, and bring mixture to the boil over medium heat. Boil for one minute, stirring constantly. In small bowl, with a wire whisk, beat egg yolks until smooth. Whisk in a small amount of the hot lemon mixture. Pour the egg mixture into the sauce pan, beating the hot lemon mixture rapidly. Reduce heat to low; cook, stirring constantly, 5 minutes, or until thick (don't allow it to boil).
Pour mixture into medium bowl. Press cling film onto surface to keep skin from forming as it cools. Cool to room temperature. Refrigerate for 3 hours.
To make the icing: In large bowl, beat icing sugar, 115g butter, 2 tablespoons lemon juice and 1 teaspoon lemon zest until smooth. Beat in milk, and increase speed and continue to beat until light and fluffy.
To assemble: With long serrated knife, split each cake layer in half horizontally, making 4 layers. Place 1 layer, cut side up, on a serving plate. Spread with half of the lemon filling. Top with another layer, and spread with some icing. Add third layer, and spread with remaining lemon filling. Press on final cake layer, and cover the top and sides of cake with remaining icing. Keep cake covered and in the fridge until serving time.
How to ice a cake video
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