Preheat your oven to 200F. On a baking pan, place a sheet of parchment paper and add the castor sugar on it. Put in the oven for about 15-20 minutes. This will help the sugar to dissolve in the egg whites later.
In a very (very) clean bowl, add the egg whites. Make sure there is no egg yolk in them. Start beating the egg whites using a hand mixer on the lowest speed. You want to build the foam slowly. Initially you will see big bubbles which will soon become finer. At this point the egg whites would have considerably increased in volume.
Now you can increase the speed of your blender and keep beating until your egg whites reach the stiff peaks stage. Stiff leaks is when you lift off your whisk from the eggs, the peaks that are formed on the egg whites would hold their shape and would not collapse into the rest of the eggs whites.
By this time, your sugar would be ready. Take it out of the oven and transfer it to a bowl.
Add the sugar to the egg whites one spoon at a time. Between each addition, make sure you mix and dissolve the sugar properly. Take your time doing this. Be patient. I take 7 minutes in total to do this.
By the end of this, your meringue will look glossy and very smooth. Your meringue is almost ready. Add the food flavoring and mix gently.
Meringue is ready. Transfer to a piping bag and pipe the shape of roses. I used Wilton tip 2D.
Bake in a 200F oven for 1 hour 30 minutes to 1 hour 45 minutes. When the meringue cookies are ready, they will come off the parchment paper easily.
Let them cool down completely in the oven for the next few hours. Enjoy!
Keep them stored in an airtight container and try to finish all within 10 days.