Braised Scallions from Molly Stevens - Cooking by the Book

Ingredients

• 1 cup shelled pistachios
• 2 ½ tablespoons unsalted butter, at room temperature
• 1 pound scallions (about 5 bunches, or 3 dozen)
• ½ cup water
• 1 ½ teaspoons coarsely chopped fresh tarragon (do not substitute dried) or 1 tablespoon chopped flat-leaf parsley
• Coarse salt and freshly ground black pepper
• 1/2 lemon