Heat your oven to 400degreesF Line 2 flat baking sheets and a deep baking tray with baking parchment.
Place the caster sugar in the deep baking tray in the oven for 7 minutes.
Place the egg whites in a stand mixer on the slowest speed and start whisking. Gradually increase the speed until soft peaks form and the sugar is ready. Take the sugar out of the oven-it should be hot but not caramelized. Turn the temperature down to 200°F.
Slowly add the sugar to your eggs with the mixer on full speed, one spoon at a time. Be careful not to add the sugar too quickly or your eggs will deflate.
Once all the sugar has been added, keep the mixer going for a minute longer until the mixture looks thick and glossy. A good way to check if it is done is to dip the whisk into the mix to see if it creates a peak once pulled out.
Divide the mixture between 4 bowls and carefully fold in the powdered food color.
Scoop the mixture into 4 piping bags fitted with round and star nozzles. Pipe your monsters onto the baking sheets and add sprinkles.
Bake for 1 hour until the meringue comes away from the baking parchment clean and the base is firm.