Preheat the oven to 375°F.
For the filling, melt the butter in a small pan over medium heat, then cook the scallions until soft and translucent, 3 to 5 minutes. Transfer to a large bowl and let cool.
Thoroughly drain the spinach of all water by squeezing it in a cheesecloth. (Wet spinach will cause your spanakopita to be soggy.)
Add the spinach dill salt pepper eggs, cottage cheese, feta cheese, and olive oil to the
bowl containing the scallions. Fold the ingredients together until fully combined, being careful not to break up the feta. Set aside.
For the dough, using the melted, clarified butter, lightly butter a 10-by-15-inch baking dish or baking sheet. Remove the phyllo from the package, unfurl each piece, and lay flat. You should have around 25 to 30 sheets. As you work, cover the flattened dough sheets with a damp tea towel or moistened paper towel to prevent them from drying out.
Carefully peel off one sheet of phyllo and lay it on the bottom of the dish. Do not straighten or pull tight. With a pastry brush, generously spread clarified butter over the sheet until it is moistened. Continue laying down sheets and coating with butter until you have used half of your total phyllo dough (10 to 15 sheets).
Spread the spinach filling over the sheets of phyllo in an even layer, to the edges of the dish. Layer the remaining phyllo sheets, brushing with butter between each layer, until 3 sheets of phyllo remain. Place the final sheets on top together, tightly, to create a smooth top. Brush the top with clarified butter to finish.
Using a very sharp paring knife, score 4 even lines lengthwise down the phyllo about
½ inch deep. Then cut five even lines across horizontally, to create 30 rectangular pieces. Cut a diagonal line across each piece to create triangles. Nelly likes to cut the corner pieces in opposite directions.
Brush clarified butter into each cut. This keeps the fillo in place while cooking. Using the paring knife, carefully tuck the borders down by running the knife around all 4 edges. Brush the borders with butter.
Bake for 1 hour, until the top is a deep golden brown. (Check after 45 minutes to assess the level of browning. If it is already dark brown, cover with foil for the last 15 minutes of cooking.) Let cool; serve at room temperature.