Pre-heat the oven to 180°C/160°C /Gas Mark 4. Line a muffin tin with 12 Muffin Cases. Place the butter and sugar in a large bowl and cream together until light and fluffy.
Add the eggs and Lemon Extract and beat together until smooth, if the mixture begins to curdle add a spoonful of flour. Fold in the flour until combined.
Divide the mixture between the Muffin cases and bake for 15-20 minutes until risen and golden brown. Allow the cupcakes to cool in the tin for 10 minutes and then transfer to a cooling rack to cool completely.
Whilst the cupcakes are cooling make the buttercream, place the butter in a large bowl and beat with an electric mixer until smooth and glossy. Add 1/3 of the icing sugar to the butter and beat until combined, continue adding another 1/3 of the icing sugar mixing until combined and then add the remaining icing sugar. Add the Lemon Extract and beat the buttercream until it is light and fluffy in texture.
Place the buttercream in a piping bag fitting with an open star nozzle.
Once the cupcakes are cool, take a sharp knife and cut a circle out of the top of each cake at an angle about 2cm from the edge. Remove the circle of sponge and place a small spoonful of lemon curd in the hole in the sponge and place the piece of sponge back on top. Repeat to fill each cupcake with lemon curd.
Pipe a swirl of buttercream onto the top of each cupcake.
Drizzle a small amount of lemon curd onto each cupcake and top with a small slice of lemon.