Add flour and salt to a large bowl or food processor. Mix in 1 T. chunks of butter and work together or pulse until well-blended.
Add one tablespoon of water at a time and keep working the dough until all the water has been added.
Form into a large bowl and refrigerate until ready for an hour or until you are ready to use.
In a large sauté pan over medium heat, add 2 tablespoons of olive oil, onions, and sauté until soft but not brown.
Add garlic and sauté for another minute until fragrant.
Add leeks and spinach and cook until wilted.
Remove from heat, put in a large bowl, and allow to cool for 5 minutes.
Stir in dill, salt and pepper, parmesan cheese, crumbled feta and one egg.
Place dough on wax paper or a floured surface and press down with your hands, continue to roll out with a rolling pin to a 10-12" diameter.
Transfer to a parchment-lined sheetpan.
Place the spinach and leek mixture in the center of the dough.
Working from the outer edges; begin folding small sections inward to the center, there center should be uncovered.
Make the egg wash with 1 egg and 2 T milk. Brush on the dough.
Bake in a 400-degree oven for 1 hour or until the bottom and top are evenly browned.
Allow to cool for 15 minutes. Serve warm or cold.
