Sift together almond flour, pistachio flour, and powdered sugar into a large bowl and set aside.
In a stand mixer fitted with the whisk attachment, whisk the egg whites on medium speed until they become foamy, then add in the cream of tartar.
Turn the mixer up to medium-high and gradually add in the granulated sugar (make sure to add the sugar in very slowly so that the meringue doesn’t deflate). Once all the sugar is added, turn the mixer to the highest setting and whisk on high until soft peaks form.
Add in the green gel food coloring and continue to beat on high until stiff peaks form.
Using a spatula, gently fold in half of the dry ingredient mixture until fully combined. Then gently fold in the remaining dry ingredients. Continue to gently fold the batter until it reaches a “flowing lava” consistency. You should be able to make a “figure 8” with the batter before it breaks. As soon as you reach this consistency, stop mixing! If you over-mix the batter, the macarons won’t rise properly in the oven.
Line a large baking sheet with a silicone mat or parchment paper.
Scoop batter into a large piping bag fitted with a round tip. Hold the piping bag perpendicular to the silicone mat and pipe 1 inch rounds.
Pick up the baking sheet and drop it onto the counter 3-4 times to help bring any air bubbles to the surface of the macarons. Then use a toothpick to pop any visible air bubbles to make a smooth surface.
Let the macarons sit at room temperature for 30-40 minutes or until a skin forms on the surface. You should be able to lightly touch the surface without any batter being disturbed.
While the macarons are resting, preheat the oven to 300°F.
Bake one sheet at a time on the center rack of the oven for 15 minutes or when they do not move on their “feet” when touched.
Let the macarons cool completely on the baking sheet before removing them. They should easily peel off when fully cooled.
Match up your shells before filling, and then turn one side over. On the other side, drizzle a small amount of white chocolate over the top and sprinkle with leftover ground pistachios (you only need a tiny bit so just use some of the white chocolate from the ganache).
White Chocolate Ganache
Finely chop the white chocolate and place into a large bowl.
Place the heavy cream in a microwave safe bowl and microwave for 1-2 minutes or until hot to the touch but not boiling.
Pour over the chopped white chocolate and let sit for about two minutes.
Using a spatula, gently mix until the chocolate is fully melted and the ganache is fully combined and smooth.
Let sit at room temperature or in the fridge until is has thickened enough to hold its shape.
If your ganache is too firm, microwave for 10 seconds to soften and then stir until ganache is the desired consistency.
Once the macarons are cooled and decorated. Pipe the ganache in the center of the undecorated shell, leaving a little bit of room on the sides. Sprinkle some leftover ground pistachios over the ganache, then top with the decorated shell.
Put the assembled pistachio white chocolate macarons in an airtight container, then place them in the fridge to mature for 12-24 hours. Store in the fridge for up to 5 days. However, for the best taste/texture, let them come up to room temperature for about an hour before eating! [Directly out of the fridge they can sometimes be super hard but at room temperature they're perfectly soft and tender!]
Notes
To make pistachio flour
Place ½ cup of pistachios is a small food processor.
Pulse a few times until the pistachios start to become ground but be careful to not pulse too much or the pistachios will start to release their oils and become more of a paste than a flour.
The flour will still be very lumpy but that's fine. Sift the ground pistachios and then place the big pieces that are leftover back in the food processor and pulse again. You want the sifted pistachio flour to be about the same size/texture as the sifted almond flour.
You only need 15 grams (about 2 tablespoons) of the sifted pistachios for the macaron shells. Once you have enough of the finely ground pistachios for the shells, set aside the larger chunks to use later.