Line two large baking pans with parchment paper or Silpat mats. 

Heat a small saucepan of simmering water over medium-low heat.

Add the egg whites and granulated sugar to a heatproof bowl and set it over the simmering water.

Whisk constantly until the sugar has fully dissolved, about 2 minutes. 

Transfer the egg mixture to the bowl of a stand mixer fitted with the whisk attachment and beat on medium-high speed until stiff peaks form, about 5 minutes. 

Using a fine-mesh sieve, sift the powdered sugar and almond flour into the egg white mixture, making sure to discard any large lumps.

Gently fold the dry ingredients into the egg whites, making sure not to deflate the egg whites at this point. 

Once all of the dry ingredients have been incorporated, add the gel food coloring, if using. (see notes)

Continue to fold the meringue but this time gently smush the batter against the sides of the bowl before folding it back together.

Continue to smush and fold the meringue a few times before testing to see if it has reached the Figure 8 stage. The meringue is ready to pipe when you can draw a figure 8 without the stream breaking. 

Transfer the meringue to a piping bag fitted with a small round tip (Wilton #10).

Pipe 1” macaron shells onto the tray, making sure to pipe them at least 2” apart.

Once you’ve finished piping the first tray, hold it a few inches off the counter and drop it straight down. Drop the tray another 5-6 times, or until it looks like any large air bubbles have popped. Repeat with the second tray. 

Set the trays aside to rest for at least 25 minutes.

They’re ready to bake when you can touch them gently without the meringue sticking to your finger. 

While the macarons rest, preheat your oven to 325 degrees F.

Bake the macarons, one tray at a time, for 13 minutes. If your oven has hot spots, make sure to turn the tray halfway through baking so the feet rise evenly. 

Allow the macarons to cool to room temperature before trying to remove them from the pan. This will help prevent sticking. 

Add the butter to the bowl of a stand mixer and beat on medium-high speed until the butter is light in color, about 2 minutes.

Turn the mixer to low speed and add the powdered sugar slowly followed by the vanilla extract.

If the mixture seems too dry, add a tablespoon of heavy cream or milk. 

Turn the mixer to high speed and beat until the buttercream becomes light and fluffy, about 2 minutes. 

Transfer the mixture to a piping bag fitted with your choice of tip. Set aside until ready to use. 

Place the macarons in similar-sized pairs.

Pipe a small dollop of vanilla buttercream onto one of the macaron shells.

Press down gently, just until the filling reaches the edges. 

(Optional) To decorate the macarons, you can use white chocolate or food markers. Or to make the macarons speckled, combine 1 teaspoon of water with a few drops of black food coloring and use a pastry brush to splatter the food dye on the macarons (be careful not to get it on your clothes-- it stains). 

Transfer the filled macarons to an airtight container and place them in the fridge to age overnight. Bring to room temperature before enjoying.