Sieve the icing sugar and ground almonds into a large bowl and leave to one side - If you find its not sieving too well then you can whiz both in a food processor to ground the almonds down slightly more, to then sieve - but it’s VERY important to sieve them!
Using an electric whisk, whisk up the egg whites until they're thick and foamy and starting to form soft peaks.
Gradually add the caster sugar 1tsp at a time, whisking in-between each addition fully, until all of the caster sugar is incorporated.
Once all of the sugar is incorporated continue to whisk for 1-2 minutes, and start adding your food colouring! (I used the Dr Oetker Neon Orange Gel) and whisked it in whilst adding. Keep on whisking for 3-4 minutes until its smooth and light.
The meringue mixture will be quite runny but reasonably thick, but this is expected! Once finished, fold the mixture into the icing sugar/almond mix - try to be gentle and use as little mixing as possible. I do mine in about 20 folds!
Using a piping bag and a round nozzle, pipe the macarons onto a lined baking tray - they end up being about 1" in width. (The mixture is quite runny, so be careful that it doesn't go everywhere or you make the shells too big!)
Tap the macaron trays onto the work surface several times so that you knock out the air bubbles and leave the macarons on the side for ONE HOUR so that a skin is formed.
Preheat the oven to 130ºC and bake the macarons for 15-18 minutes until they have risen to have their "feet" and are starting to peel away from the tray - leave them to cool fully before trying to remove them.
Buttercream Filling and Decorating
Beat the unsalted butter, icing sugar, and food colouring together like you would a normal buttercream and prep it for decorating.
Once the shells have cooled, remove them carefully from the trays and line them up - melt your dark chocolate and drizzle some on, sprinkle with the halloween sprinkles, then leave to dry.
Once dry, pipe or spread on some of the orange buttercream onto half of the shells and sandwich the macaron shells together, then chill them in the fridge for an hour. Enjoy!
Notes
The Macarons last for up to 7 days in an airtight container in the refrigerator, or you can freeze the unfilled shells for up to 3 months!