Make the Pistachio Ganache
Combine the heavy cream and pistachios in a small saucepan.
Heat over medium heat until the cream begins to simmer.
Immersion Blender Method (Recommended)
Pour the hot cream and pistachios into a medium bowl.
Add the white chocolate, ensuring it is fully submerged.
Let sit for 2 minutes, then blend with an immersion blender until smooth and the pistachios are finely broken down.
Food Processor Method
Transfer the hot cream and pistachios to a food processor or blender and blend until smooth.
Pour into a bowl and add the white chocolate.
Allow the chocolate to melt for 2 minutes, then stir until smooth.
Add a drop of green food coloring and a pinch of salt if desired.
Cover with plastic wrap pressed directly onto the surface.
Refrigerate for about 2 hours, or until pipeable.
Prepare the Macaron Shells
Line two baking sheets with silicone baking mats or parchment paper.
Finely grind the pistachios in a food processor until dry and powdery. Avoid over-processing.
Sift the ground pistachios through a fine mesh sieve and set aside.
In the bowl of a stand mixer, whisk the aged egg whites until foamy.
Add the cream of tartar and continue mixing until soft peaks form.
Gradually add the granulated sugar while mixing on medium-low speed.
Increase the speed to medium-high and beat until stiff, glossy peaks form.
Make the Macaron Batter
Sift together the almond flour, powdered sugar, and ground pistachios.
Add the dry ingredients to the meringue.
Add green food coloring if desired.
Fold gently using a spatula until the batter flows in thick ribbons and can form a figure-eight without breaking.
Pipe and Rest
Transfer the batter to a piping bag fitted with a round tip.
Pipe 1½-inch rounds onto the prepared baking sheets.
Firmly tap the trays on the counter several times to remove air bubbles.
Pop any visible bubbles with a toothpick.
Let the macarons rest for 30 minutes, or until a dry skin forms.
Meanwhile, preheat the oven to 157°C (315°F).
Bake the Macarons
Bake one tray at a time on the middle rack for 18–21 minutes.
Rotate the tray halfway through baking for even results.
Allow the shells to cool completely before removing them from the baking mats.
Pair shells of similar size together.
Assemble the Pistachio Macarons
Transfer the chilled ganache to a piping bag.
Pipe a dollop of ganache onto one shell.
Gently sandwich with a second shell.
Optional: Drizzle with melted white chocolate and sprinkle with chopped pistachios.
Mature the Macarons
Place assembled macarons in an airtight container.
Refrigerate overnight to allow flavors and textures to develop.
Bring to room temperature for 15 minutes before serving.