Place a pan over a medium heat and allow to get very hot. Add some olive oil, the spinach, spring onions. Mix with a wooden spoon and sauté, until the greens wilt.
Transfer to a bowl and add the feta cheese, dill and mint. Season with salt and pepper and mix thoroughly. Pour the filling into a colander with a bowl underneath to drain the liquids and let it cool.
Dust a clean working surface with some corn starch and fill a bowl with some corn starch. Take one of the balls of dough and dip it into the bowl with the corn starch and spread it out a little with your hands. Place it on the work surface. Use a long rolling pin to roll out the dough. Begin from the outer border and roll inwards towards the center.
Turn the dough clockwise, and repeat the same process continuously, until you have created a very thin phyllo dough that is 35 cm (14 inches) in diameter. Repeat the same process for the remaining balls of dough.
Brush a 30 cm (12 inches) round baking pan with some olive oil. Add 3 sheets of phyllo dough, brushing each one with olive oil.
Add 1/3 of the filling and spread evenly over the phyllo dough. Cover with 1 sheet of phyllo and brush with olive oil. Add another 1/3 of the filling over it.
Cover with 1 sheet of phyllo and brush with olive oil. Add the remaining filling, spread evenly and add 2 more sheets of phyllo dough, brushing each one with olive oil.
Fold the overhanging edges inward to create a border and lightly score the surface with a straight edged knife and brush with olive oil.
Bake the spinach and cheese pie for 1 hour, until it is golden and the phyllo is crunchy. Serve hot.