Divide saffron powder into two batches. Add 50 ml warm water (approximately 4.5 tbsps) to one batch, stir and set aside. Leave the other batch as is, in powdered form. You will use it later.
Pat leeks dry before you begin to cook.
Place a large frying pan (I use this one, which is 30cm / 12in) on the stove on medium heat and add oil. When oil is hot and glistening, add leeks and sauté till they begin to wilt a bit, just about 5-7 minutes. Do not brown or overcook leeks.
Turn heat to medium-high and add shrimps and saffron water. Sauté till the shrimp shells turn pink, about 3-4 minutes. Add herbs, gently stir to combine, take pan off stove and set aside.
Working very quickly (you don't want the shrimps to completely cool down), place a small saucepan or frying pan on high heat and add butter. As soon as butter begins to melt, add the reserved powdered saffron, stir and pour this saffron-butter over shrimps. Gently stir to combine.
Sprinkle sea salt on top and serve immediately.
Enjoy with your choice of bread.