Pre-heat oven to 120 degrees C. Line a baking tray with some baking paper.
Wash the limes with hot water and finely grate the peel.
Squeeze the juice out of the 1/2 lime.
Using a Braun hand mixer beat the egg whites with the salt untile stiff, then slowly add the sugar.
Beat until glossy peaks have formed. Carefully fold in the almond powder and the zest of 1 lime.
Fill the mixture into piping bags with a plain tip and pipe out small circular dots on the baking tray.
Bake in the oven for 60 mins, making sure they do not brown. Bake the baisers until crispy. Allow to cool.
In the meantime whisk together the confectioner's sugar with the butter until a thick, smooth and creamy mixture is formed. Add in the remaining lime zest and 2-3 tablespoons of lime juice.
Assemble the cookies by spreading the lime buttercream on the bottom of a baiser and then close with a second. Gently press together.