Preheat the oven to 300°F (150°C). Line a baking sheet with parchment paper.
Sift almond flour and powdered sugar together.
In a separate bowl, beat egg whites until foamy. Add cream of tartar and beat until soft peaks form. Gradually add granulated sugar and beat until stiff peaks form.
Fold the dry ingredients into the egg whites until the batter flows like lava. Add food coloring if desired.
Transfer the batter to a piping bag and pipe small circles onto the prepared baking sheet. Tap the sheet on the counter to release air bubbles.
Let the macarons sit at room temperature for 30 minutes to form a skin.
Bake for 15 minutes, rotating the sheet halfway through. Let cool completely.
For the filling, beat the butter until creamy. Gradually add powdered sugar and pistachio paste, beating until smooth.
Pipe the filling onto half of the macarons and sandwich with the remaining shells.