For the Salmon:
In a shallow dish, combine the pistachios, 1/2 teaspoon salt, and pepper. Dredge the salmon in the pistachio mixture, pressing gently to coat.
In a small skillet, heat the oil and garlic over medium heat. Add the salmon and cook until browned, about 2 to 3 minutes. Reduce the heat to medium; turn the salmon and cook until salmon flakes easily with fork, about 2 or 3 minutes more. Transfer the fillets to serving plates. Serve with Lemon Cream Sauce, and garnish with chopped pistachios, if desired.
For the Lemon Cream Sauce:
In a small saucepan, melt the butter over medium-high heat. Add the flour, whisking to combine and cook for 2 minutes. Reduce the heat to medium; stir in the broth and cream and simmer until thickened, whisking frequently, about 3 minutes. Add the lemon zest, lemon juice, 1/2 teaspoon salt, and pepper, whisking to combine. Cook for 2 minutes, whisking constantly. Pour into a serving dish and serve with the salmon.