Preheat the oven to 150 degrees C
Place egg whites and cater sugar in a bowl and mix with electric mixer for 8-10 minutes (yes really), add gel food colouring and continue to mix for a further 30seconds. The mixture should look stiff and dry.
Sift the almond meal and icing sugar and salt twice, discarding any almond lumps that are too big to pass through the seive. Fold into the egg white mixture. It should take roughly 50 folds until the mixture is smooth and a very viscous liquid, 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 video for examples (troubleshooting is at the end of video). 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 cleanly, if not bake for longer – if they are looking done on top move to the bottom shelf of the oven for the remaining time to help bake the base.