Preheat the oven to 155'C.
Whisk the egg whites with 150g caster sugar and the food colouring. Whisk until you have a stiff and glossy meringue mixture.
Place the icing sugar and the almond powder in a blender. Blitz and then sieve this mixture into a bowl to ensure that you have a very fine, lump-free powder.
Incorporate the dry ingredients into the meringue mixture. Use a spatula to cut and fold the mixture until is smooth, shiny and ribbon-like.
Fill a piping bag with the macaroon mix and pipe the macaroons onto a lined baking tray. Leave the macaroons to dry slightly for 15minutes at room temperature and then bake in the preheated oven for 10-15minutes.
Zest half of the lemon then cut in half and squeeze the juice from one half.
Sift the icing sugar in to a bowl then add the softened butter, lemon zest and lemon juice. Beat together until you have a thick buttercream.
Fill half of the macaroon shells with the lemon buttercream and then top with a second macaroon shell.
Serve with a light dusting of icing sugar.
«For a super tangy buttercream, add a little more lemon juice. If in season, add a raspberry to the centre of each macaroon for an extra fruity treat!»