Spanakopita Greek Spinach Pie

Name: Spanakopita (Greek Spinach Pie)
Ingredients: 6 lb. fresh spinach, washed in several changes of water and coarsely chopped; 4 tbsp. extra-virgin olive oil; 2 large yellow onions, finely chopped; 2 bunches scallions, trimmed and thinly sliced; 1⁄2 cups finely chopped fresh dill; 1⁄2 cups finely chopped fresh parsley; 1⁄4 lb. feta, crumbled; 1⁄4 cups long-grain rice; Kosher salt and freshly ground black pepper; 1⁄2 lb. frozen phyllo dough, thawed; 6 tbsp. unsalted butter, melted, plus more for greasing