Preheat your oven to 160 °C and line your baking sheet with parchment paper.
Whip eggs and sugar together for about 5 minutes.
Add rosewater and fold in pistachios.
Whisk flour and baking powder and add gradually to the wet ingredients.
Shape a log about 8 cm wide.
Bake for 30 minutes at 160 °C. Cool the logs on the baking tray for 20 – 30 minutes until cool to touch but still a bit warm.
Transfer to a cutting board and slice at an angle with a serrated knife. Each slice should be just over 1 cm thick, but thickness is totally up to your preference.
Place back in the baking tray, leaving space between them. Return to the oven and bake for additional 15 minutes.