How to Make It
In a small bowl, combine the Madeira, lemon juice, mace, piment d'Espelette and 1 1/2 teaspoons of salt; mix well. Let the spice mixture stand at room temperature for 10 minutes, then mix in the butter.
In a small bowl, combine the parsley, lemon zest and garlic. Season the shrimp with salt and pepper. In a large skillet, heat 2 tablespoons of the olive oil. Add half of the shrimp and cook over moderately high heat, turning once, until golden brown and just cooked through, 2 to 3 minutes per side. Add 2 tablespoons of the spiced butter to the skillet and cook until lightly browned; add 1 tablespoon of the lemon juice and toss to coat the shrimp in the sauce. Using tongs, transfer the shrimp to a serving platter. Strain the butter sauce through a sieve into a small bowl. Repeat with the remaining olive oil, shrimp, lemon juice and 2 more tablespoons of the butter. Season the butter sauce with salt and drizzle it over the shrimp. Top with the gremolata and serve.
Piment d'Espelette is a mildly spicy, ground red pepper. It's available at specialty food shops, or at zingermans.com.