Step 1Leaving the water on the spinach leaves after washing, place the spinach in a large (14-inch) heavy nonstick skillet and cook over medium-high heat until wilted, about 4 minutes. Transfer to a colander, rinse with cold water and press out as much water as possible. Then wrap the spinach in a towel and squeeze out more water. Chop fairly fine and set aside.(This can be done in advance. The wilted spinach will keep for 3 or 4 days in the refrigerator.)
Step 2Heat 2 tablespoons of the olive oil in the same skillet over medium heat and add the leeks. Saute, stirring often, until softened and just beginning to brown, about 10 to 15 minutes. Add the spinach and stir together until the spinach is coated with oil. Remove from the heat. (You can make the recipe through this step several hours or a day ahead. Store in the refrigerator in a covered bowl. )
Step 3Place the combined spinach and leeks in a large bowl. Stir in the chopped parsley, dill, beaten eggs, feta cheese, salt, pepper and nutmeg.
Step 4Brush an 11-inch tart pan with olive oil and layer in 7 sheets of phyllo dough, one at a time. Brush each sheet with olive oil before adding the next sheet. Place them not quite evenly on top of one another so that the edges overlap the sides of the pan all the way around. (When working with phyllo dough, work with one sheet at a time. Keep the other sheets covered with a slightly damp cloth to prevent them from drying out.) Press around the edge of the pan so the phyllo dough fits into the bottom of the pan.
Step 5Spoon the spinach mixture onto the phyllo dough, spreading it evenly over the bottom of the pan.
Step 6Using kitchen scissors, trim the edges of the dough to a 1 1/2 -inch overhang. Fold the edges of the dough over the spinach mixture and brush them with olive oil. Layer 5 more sheets of dough over the top, brushing each sheet with olive oil. Using scissors, cut the excess dough to a 1 1/2 -inch overhang and tuck the edges under into the sides of the pan.
Step 7Brush the top of the pie with olive oil, and the beaten egg white, and pierce in several places with a sharp knife. (The spanakopita can be assembled a few hours before you bake it and held in or out of the refrigerator.) Place the pie on a baking sheet and bake at 375 degrees until golden brown, about 45 to 50 minutes. Serve hot or at room temperature.