- 1 (10-oz) package frozen chopped spinach
- 1 cup chopped scallions
- Salt
- 1 tablespoon olive oil
- 1/4 pound fresh sorrel leaves, chopped (2 packed cups)
- 1 egg yolk, lightly beaten
- 8 ounces feta, crumbled (1 cup)
- 1/4 teaspoon ground nutmeg
- 3 tablespoons chopped fresh dill, or to taste
- Freshly ground black pepper
- 10 (17- by 12-inch) sheets phyllo, thawed if frozen
- 1 1/2 sticks (3/4 cup) unsalted butter, melted
- Cook spinach according to package instructions. Drain in a colander, then refresh under cold running water to stop the cooking, and drain well again. Transfer spinach to a clean kitchen towel (not terry cloth) twisting the ends together, and squeeze as much liquid as possible from the spinach. Transfer spinach to a large bowl.
- Cook scallions with 1/4 teaspoon salt in olive oil in a 9- to 10-inch non-stick skillet over medium heat, stirring, until softened, 2 to 3 minutes. Add sorrel and cook, stirring and adding 1 tablespoon water if sorrel is dry, until wilted, about 1 minute (sorrel will turn khaki gray almost immediately when heated). Add sorrel mixture to spinach and stir well.
- Stir in yolk, then feta, nutmeg, dill, and salt and pepper to taste and combine mixture well.
- Preheat oven to 375°F. Line a large rimmed baking sheet with parchment paper.
- Cover phyllo stack with 2 overlapping sheets of plastic wrap and then a dampened kitchen towel.
- Take 1 phyllo sheet from stack and arrange on a work surface with a long side nearest you (keeping remaining sheets covered) and brush all over with some butter. Cut buttered phyllo stack lengthwise into 4 strips, each about 3-inches wide and 17- inches long.
- Put a heaping teaspoon of filling near 1 corner of a strip on end nearest you, then fold corner of phyllo over to enclose filling and form a triangle. Continue folding strip (like a flag), maintaining triangle shape. Brush triangle all over with butter. Put triangle, seam side down, on parchment-lined sheet. Make more triangles in same manner, using all of phyllo.
- For best results, freeze spanakopita until firm, about 20 minutes.
- Bake triangles in middle of oven until golden brown, 20 to 25 minutes, then transfer to a rack to cool slightly.