Place egg whites and cater sugar in a bowl and mix with electric mixer until stiff enough to turn the bowl upside down without it falling out, continue to whip for 1-2 more minutes. How long this takes will depend on you mixer. Add gel or powdered food coloring and continue to mix for a further 20seconds.
Sift the almond meal and icing sugar and salt twice, discarding any almond lumps that are too big to pass through the sieve. Fold into the egg white mixture. It should take roughly 30-50 folds using a rubber spatula. The mixture should be smooth and a very viscous, not runny. Over-mix and your macarons will be flat and have no foot, under mix and they will not be smooth on top – see the macaron troubleshooting post for examples.
Pipe onto trays lined with baking paper, rap trays on the bench firmly (this prevents cracking) and then bake in the oven for 20 minutes. Check if one comes off the tray fairly cleanly, if not bake for a little longer (make sure you are using NON-stick baking paper or they will stick).