Process icing sugar and hazelnut meal in a food processor until finely ground. Triple-sift into a large bowl and set aside.
Whisk 90 grams of the egg whites in an electric mixer until soft peaks form (about 1-2 minutes). Add caster sugar, a tablespoon at a time, whisking continuously until incorporated and mixture is thick and glossy (2-3 minutes), then add food colouring.
Stir in hazelnut mixture in batches until incorporated and mixture slowly slides down sides of bowl when bowl is tilted. Add remaining eggwhite to loosen mixture.
Spoon into a piping bag with a 1cm plain nozzle, pipe 3cm-diameter rounds of mixture onto baking-paper-lined oven trays, stand until a crust begins to form (I left them for 2 hours but you can leave up to 5 hours if you have the time).
Preheat oven to 140°C. Bake macarons until firm but not coloured, swapping trays halfway through cooking (10-12 minutes), set aside, cool completely on trays.