How to Make It
Put the barberries, if using, in a small bowl of water and leave to soak for 5 minutes, then drain. Use paper towels to pat out as much moisture as you can from the soaked barberries and the herbs.
Whisk the eggs vigorously in a large bowl with the baking powder, advieh, softened butter, herbs, barberries and walnuts, if using, and season with salt and pepper.
Melt the remaining butter in an ovenproof, nonstick frying pan over high heat. When the butter begins to foam, pour in the egg and herb mixture and stir well, then reduce the heat and cook for 15 minutes until well-risen and almost fully set on top. Sprinkle with the feta. Meanwhile, preheat the broiler to high.
Place the pan under the broiler and leave for about 5 minutes until golden on the top and just cooked.
Transfer to a plate and sprinkle with dried rose petals, if you like. Serve immediately with warm flatbread, lime wedges and yogurt.