1/2 stick butter
1 10oz package frozen spinach
1 scant cup crumbled feta
1/2 teaspoon freshly grated nutmeg
12 (14- by 9-inch) phyllo sheets, thawed
1/2 teaspoon salt
1/2 teaspoon pepper
Thaw spinach by placing in a skillet over low heat, separating as it thaws. Cook for a minute or two more to remove excess water. Remove from heat and cool. Transfer to a bowl and stir in feta, nutmeg, 1/2 teaspoon salt, and 1/2 teaspoon pepper.
Preheat oven to 375°F.
Melt butter, then cool.
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 short side nearest you (keeping remaining sheets covered) and brush with some butter. Top with another phyllo sheet and brush with more butter. Cut buttered phyllo stack in half lengthwise.
Put a scant tablespoon 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. Put triangle, seam side down, on a large baking sheet and brush top with butter. Make more triangles in same manner, using all of phyllo.
Bake triangles in middle of oven until golden brown, 15 to 20 minutes.
Note: Pastry triangles can be formed, but not baked, 3 days ahead. Arrange in 1 layer in heavy-dty sealed plastic bags, then freeze. Bake frozen pastries(do not thaw) in same manner as above.