Beat the egg whites with a pinch of salt until stiff. Fold in the ground almonds, pistachios and flour and mix until smooth and moldable, adding a bit more flour if needed. Preheat the oven to 150°C (approximately 300°F). Line a baking sheet with parchment paper.
Using wet hands, shape the mixture into small, oblong patties and place onto the prepared baking sheet. Press a few shelled pistachios onto each pattie and bake for 10-15 minutes, until golden brown. Remove from the oven, cool on a wire rack and dust with powdered sugar before serving.