Preheat the oven to 180°C/Gas Mark 4.
Cream the butter and caster sugar together until the mixture is pale and light. This is easiest using a free-standing mixer and will take about 3-4 minutes on medium speed.
Gradually add the beaten eggs, mixing well between each addition and scraping down the sides of the bowl from time to time. Add the vanilla extract and mix again.
Sift the flour and salt into the bowl and fold in using a large metal spoon or rubber spatula until the mixture is glossy and smooth.
Divide the mixture between a Lakeland 12-hole Mini Sandwich Pan (roughly 1 heaped dsp mixture in each well) and level with a teaspoon.
Bake on the middle shelf of the oven for about 15 minutes until golden, well-risen and a wooden skewer inserted into the middle of the cakes comes out clean.
Leave the cakes to rest in the tin for 2 minutes, then carefully ease out onto a wire cooling rack until cold.
To make the buttercream, cream together the butter, icing sugar and vanilla extract until pale and light.
Cut each of the cakes in half and spread the bottom layer with buttercream. Top with a teaspoon of lemon curd and sandwich with the top cake layer. Lightly dust with icing sugar.