Preheat the oven to 180°C / 350°F.
Whisk the egg whites lightly for 20 seconds, until fluffy. Add in almond extract.
Chop the pistachios finely, or blitz in a food processor until in small chunks. Separate away 10 g of pistachios for garnish.
Add the pistachios, almond flour, and powdered sugar into the bowl with the egg whites. Stir until combined. It should form a smooth paste.
Dollop the mixture onto a lined baking tray. It should form about 16 cookies. Place in the oven for 10 minutes or until slightly golden and crispy on the edges. Let cool for at least 10 minutes before decorating.
To decorate, melt the white and dark chocolate in separate bowls. Drizzle over the cookies in striped patterns and garnish with pistachios.