• Weigh the egg whites in a small bowl and leave them out at room temperature for at least 1 hour to come to room temperature.
• Prepare two baking sheets: Place your macaron templates onto 2 - large rimmed baking sheets with another sheet of parchment paper on top. You can lightly spray the template with non-stick spray so the top parchment paper sticks to it.
• Have several clean and dry glass bowls ready and also clean and dry your food processor, sieve, spatula, whisk/mixers, and any other equipment you'll be using.
• Use a sieve to sift the almond flour, powdered sugar, and granulated sugar, separately, and keep them in separate bowls.
• After sifting, place a clean glass bowl on your food scale, set the scale to '0' (in grams), and weigh each of the ingredients, separately, and in separate bowls. Mix the almond flour and powdered sugar in one bowl, and add the sugar to the bowl of a food processor. Pulse the sugar in the food processor for about 5 seconds until it's a very fine texture.

Make the Meringue:

• Add the room temperature egg whites and cream of tartar to a large, clean, and dry glass bowl. Use a hand-held mixer to beat the egg whites to soft peaks. This will take about one minute, the egg whites will be foamy at first and then start to thicken.
• Add the granulated sugar and continue to beat until the meringue reaches stiff, glossy peaks. About 2-4 minutes. You should be able to hold the bowl upside down without the meringue budging at all. Add the salt, vanilla extract (or another flavor extract, if using), and gel food coloring (if using), and mix until combined.

Macaronage: (Folding the macaron batter)

• Add the dry ingredients to the meringue in 3 additions and use a rubber spatula to fold in each until the batter is smooth and glossy with no pockets of flour remaining.
• After the last addition, fold just until the batter reaches the right consistency. It should be smooth, glossy, not too runny, and flow in thick ribbons from your spatula.

Pipe the Macaron Batter:

• Add the macaron batter to a piping bag with a round piping tip or with the tip of the bag cut off.
• Hold the bag vertical to the parchment paper with the tip right in the center of the circle on the template. Gently squeeze the bag until the batter spreads out and mostly fills the circle.
• Once you've piped all of the circles, lift the pan about 5" and drop it onto your counter several times to release any trapped air bubbles in the batter. The batter will spread slightly and you should see tiny bubbles of air rise to the surface and pop.

Dry the Shells:

• Before baking, you need to let the macaron shells dry out for 45 minutes - 1 hour. As they dry, they'll start to form a hard surface, you should be able to touch the tops without wet batter sticking to your finger. If they aren't dried long enough the tops of the shells will crack in the oven.

Bake the Macarons:

• Preheat your oven to 300°F and bake the macarons, one baking sheet at a time, for 10 minutes each. As the macarons bake they will form a smooth, hard surface with little feet developed underneath.
• Remove from the oven and allow the macarons to cool completely, they will be very delicate when you first take them out so don't try to touch them too soon.
• Let the macarons cool completely before removing from the sheet. You can place the entire baking sheet in the freezer for about 10 minutes, which makes it much easier to take them off of the parchment paper without breaking.

Vanilla Buttercream Filling:

• In a medium bowl, use a hand-held mixer to beat the softened butter, powdered sugar, heavy cream, vanilla extract, and salt until smooth.
• Pipe or spread the filling onto the bottom of one shell, then take a second shell that's close to the same size and gently sandwich the two together.