Preheat the oven to 190℃ / Fan 170℃ / Gas 5. Place the muffin sized cases into the muffin tray.

Place the soft
butter and sugars into a good sized bowl and beat together with a wooden
spoon or electric beaters until very pale and fluffy. Add the salt and
beat again to combine. Gradually add the beaten eggs a little at a
time, beating well after each addition. Beat in 3 tablespoon elderflower
cordial. Sieve the flour and baking powder into the mixture. Use a
spatula or large metal spoon to fold this in gently.  You're aiming for a
nice dropping consistency.  Add a little more elderflower cordial if
necessary.

Fill the muffin cases. Using a
teaspoon, fill the cases with the batter mixture. You're aiming for them
to be half to two-thirds full. You may decide to weigh each muffin to
ensure equal sizes. Each will weigh about 60g.

Bake. Place the muffin tray in the
centre of the oven and bake for about 20 - 23 minutes. You may need to
rotate the tray after 15 minutes of baking. Once baked, remove from the
oven and place on a cooling tray.

Place the
softened butter into a good sized bowl.  Beat to ensure it is soft and
creamy.  Sieve half of the icing sugar into the butter.  Use a wooden
spoon to combine the two ingredients.  Sieve in the remaining icing
sugar and mix to combine.  Beat well to create a creamy frosting.  Add
the lemon curd.  Mix to combine.  Add a little milk if necessary, and
beat in.  Spoon the mixture into a piping bag fitted with a large open
star nozzle.

 Hollow out the cupcakes.  Use a
paring knife or the wide end of a large piping nozzle to create a hollow
in the top of the cupcake.  Add some lemon curd.  Avoid over filling.
Cut off a little of the sponge and place the 'crust' piece back onto the
cupcake to act as  a 'plug'.