Line two large sheet pans with parchment paper or silpat mats.

Add the egg whites to the bowl of a stand mixer fitted with the whisk attachment. Beat the egg whites on low speeduntil they become frothy. Add the cream of tartar and turn the speed to medium-high.

Add the granulated sugar slowly, making sure that it becomes fully incorporated between each addition. It should take about 2 minutes to add all of the sugar-- try not to rush!

Once all of the sugar has been added, allow the mixer to run on medium-high speed until the meringue reaches a stiff peak.

Add the powdered sugar and almond flour to a fine mesh sieve and sift them into the egg whites. Make sure to discard any large lumps-- don’t force them through the sieve.

Using a rubber spatula, gently fold the dry ingredients into the egg whites. Try not to deflate the egg whites too much and make sure to get all the way to the bottom and scrape the sides as you fold.

Once the dry ingredients are fully incorporated (about 1-2 minutes of folding), add gel food coloring, if using.

Continue to fold the meringue together-- you can be a bit less delicate at this point. As you fold, smush the batter against the sides of the bowl and then fold it back together. Repeat the smush-and-fold for another 30 seconds before testing to see if the meringue is at the figure 8 stage. If the meringue flows smoothly while you draw an 8, it’s ready to pipe. If the stream breaks while you draw the 8, continue the smush-and-folds a few more times before retesting.

When the mixture flows smoothly, transfer the meringue to a piping bag fitted with a small round tip (I like a Wilton #10 or #12).

Hold the piping bag straight up and down and pipe small (1.5”) circles about 2” apart on the parchment/silpat linedbaking sheet.

Once you’ve finished piping the tray, hold it a few inches off the counter and drop it straight down to release any air bubbles. Repeat 5-6 times or until any large air bubbles have popped.

Set the macarons aside and allow them to rest for 30 minutes. The macarons will be ready to bake when you can touchthem gently without the meringue sticking to your finger.

While the macarons rest, preheat the oven to 325F. Bake the macarons one tray at a time for 14 minutes, turning the tray halfway through baking so they don’t get lopsided. Allow the macarons to cool fully on the tray-- if you try to remove them while warm, they may stick.

Place the pistachios in a food processor and pulse on high speed until they become a fine powder-- about 1 minute.

Place a small saucepan of water over medium-high heat and place a heatproof bowl over the saucepan.

Add the egg whites and sugar to the saucepan. Whisk continuously until the sugar has dissolved and the mixture reaches 165F with an instant read thermometer-- about 4 minutes.

Transfer the egg whites and sugar to the bowl of a stand mixer fitted with the whisk attachment.

Turn the mixer to high speed and beat until the egg whites have formed stiff peaks and are no longer warm to the touch-- about 10-12 minutes.

Next, switch the mixer to the paddle attachment and add the butter 1 tablespoon at a time, allowing it to fully incorporate before adding another piece. It’s important that both the butter and meringue be room temperature so the mixture doesn’t crack (but if it does crack, it’s easy to fix-- see notes).

Once all of the butter has been added, add the pistachios and vanilla extract and mix on medium speed just until incorporated.

Transfer the mixture to a piping bag and store in the fridge until ready to use.

Place the cooled macarons in similar sized pairs. Pipe a small dollop of filling onto the center of each macaron. Press the second macaron gently on top of the filling and press them together until the filling reaches the edge. Repeat with the remaining macarons.

Transfer the macarons to an airtight container and store them in the fridge overnight to age. Make sure to bring them to room temperature before serving.