Place the almond flour, icing sugar and blueberry powder in the bowl of your food processor and pulse for 2 minutes.
Transfer the dry ingredients to your sieve and gently sift the mixture into a bowl. Discard any large pieces of almond flour or orange zest. Place this bowl to the side.
Put your egg white into the bowl of your mixer and mix on low until bubbles start to form.
Add your cream of tartar and turn the mixer up to medium.
Gradually add the caster sugar, one tablespoon at a time, allowing the sugar to dissolve into the egg whites before adding the next tablespoon.
Add the salt and vanilla extract. Then turn the mixer up to high and whip the egg whites until they form stiff peaks.
Pour half the almond flour mixture into the egg whites and gently fold it in. Then add the remaining almond flour, and fold it in as well.
Use your spatula to deflate the batter slightly by spreading it around the sides of the bowl and the bringing it back into the middle. Continue stirring the batter in this fashion until it loosens. You will know it has reached the ideal consistency when it falls off your spatula in a ribbon shape.
Transfer the batter into a piping bag that is fitted with a round nozzle. Pipe 1.5 inch circles of macaron batter onto your prepared baking tray.
Bang your tray onto the table 3 times to encourage any air bubbles to rise to the surface, then inspect the macarons and use a toothpick to pop any visible air bubbles.
Allow the macarons to rest at room temperature until their surface turns to a mat texture and is dry to touch (may take between 15-45 minutes).
Bake in a preheated oven at 250 degrees Fahrenheit (120 degrees Celsius) for 20-25 minutes. You will know they have baked once you can peel a macaron off the baking sheet in one piece.
Once they've baked, allow the macarons to cool completely on the tray before removing them. Store in an airtight container until you are ready to assemble the macarons.