For the almond base, grind the almond slivers in a blender to a dry powder.
Add the powdered sugar in three steps.
Strain the mass through a sieve.
Then add the egg white that is at room temperature and mix to a thick batter.
Add the food coloring and the orange zest.
Boil the water and sugar in a clean saucepan over medium heat.
The sugar is boiled to 118°C. At 115°C you start turning the egg whites.
When the sugar is at the right temperature, let it fizz and pour it into the egg whites (medium speed).
When the mass has cooled back to 50°C, remove the meringue from the machine.
Add 1/3 of the meringue to the almond batter.
When the mixture is homogeneous, add the remaining meringue. The mass that is well mixed will show some toughness and will stick to the spatula.
Fill the piping bag with this (nozzle no. 9).
Pipe the macarons onto silicone mats with a diameter of 3 to 4 cm. Make sure that there is sufficient space between spraying.
Put the plates away in a dry place, so that the batter can form a thin skin (about half an hour to one hour).
Place the plates in the oven at 145°C.
After baking for 12 minutes, open the oven door for 5 seconds.
After a total baking time of 15 minutes, remove the plate from the oven and set it aside on a rack to cool gently.