Pour the aged egg whites into the bowl of a stand mixer fitted with a whisk attachment. Mix on medium speed until the surface of the egg whites is covered in small bubbles. Add in a pinch of cream of tartar and continue to mix until it reaches the soft peak stage.
Add the granulated sugar to the eggs and mix on medium speed for 30 seconds. If desired, add pink or red gel food colouring and raspberry extract at this point, then increase the mixing speed to medium-high. Keep mixing until stiff, glossy peaks form.
Sift the almond flour and icing sugar into the meringue.
Fold until a thick ribbon of batter runs off the spatula when it is lifted. You should be able to draw a couple of figure eights with the batter running off your spatula when it is the right consistency. If the stream of batter breaks before you're able to do this, you may need to stir it a bit more. The batter should reach a "flowing lava" consistency.
Streak your piping bag with lines of red gel food colouring, then fill it with the macaron batter. Pipe heart-shaped macarons onto the prepared baking sheets, using a template (draw out or print a sheet of heart shapes) to ensure they all turn out the same size.
Bang the pans firmly on the counter a few times to release air bubbles, then pop any remaining air bubbles that come to the surface with a toothpick.
Let the macarons rest for 30 minutes, or until they develop a skin and look matte. While the macarons rest, preheat the oven to 157°C.
Bake one tray of macarons at a time on the middle rack of your oven for 16-19 minutes, rotating your pan halfway through.
Remove from oven and let the macarons cool on the pan (about 15 minutes), then gently remove them from the Silpat mat.
