How to Make It
In a small saucepan, combine the orange juice, shallot and saffron. Bring to a simmer and cook over moderate heat until reduced to 1/4 cup, about 25 minutes. Transfer to a small bowl and let cool completely. Whisk in the vinegar and oil and season with salt.
Preheat the oven to 375°. Spread 2 tablespoons of the pistachios in a pie plate and toast for 5 minutes or until golden; coarsely chop. In a spice grinder, finely grind the remaining 2 tablespoons of pistachios. Season the flesh side of the shrimp with salt and pepper and coat with the finely ground pistachios.
In a large nonstick skillet, heat 2 tablespoons of the olive oil. Add the scallions and cook over moderately high heat, stirring, until lightly charred and just tender, about 3 minutes. Transfer to a plate.
Wipe out the skillet and heat the remaining 2 tablespoons of olive oil in it. Add the shrimp, flesh side down, and cook over moderate heat, turning once, until just white throughout, about 3 minutes. Transfer the shrimp to plates. Spoon some of the vinaigrette over the shrimp and top with the scallions, a drizzle of pistachio oil and the chopped pistachios. Serve the remaining vinaigrette on the side.