Prepare the crust; dissolve the salt in the water, then add the oil and stir.
Put the flour in a large bowl. Add the water mixture.
Mix the flour with a fork or knead it with you hand, until combined.
When a dough has formed, put it on a lightly-floured surface and knead it until it becomes smooth, about 2 or 3 minutes.
Form the dough into a ball, wrap with plastic film, and let sit at room temperature for about an hour.
Prepare the filling; blanch the chard and spinach in simmering water for about 3 minutes. Drain the greens and transfer onto a plate to cool.
When cool enough to handle, squeeze all the water out of the greens, until they are very dry. Chop roughly after.
Heat 2 tablespoons olive oil in large non-stick skillet over medium-high heat.
When the oil starts to ripple, add the onion and cook until it starts to turn translucent.
Add the greens to the pan, add sea salt and pepper, then mix well. Cook until the greens are tender.
Put the greens in a bowl, add the chopped marjoram and let the greens cool.
Place the ricotta in a separated bowl.
Beat 3 eggs and add them to the ricotta, following with half of parmesan cheese, parsley, nutmeg, and salt and pepper.
Whisk all the ingredients together so that the ricotta mixture is well-blended and fluffy.
Add the cooled, chopped greens to the ricotta mixture.
Prepare the hard-boiled eggs in boiling water for 10 minutes, then let them cool down.
Preheat the oven to 180°C.
Divide the dough into 2 parts, a bigger one and a bit smaller one. The big one will be the bottom and the side, the smaller one must only cover the top. Roll out pieces to 26cm in diameter and smaller one in 20cm in diameter.
Brush the bottom and sides of the baking pan well with olive oil.
Spread the larger sheet of the pastry and spread it evenly over the bottom of the pan and about up the side. It doesn't matter if it hangs over from the edge, it makes it easier to fix the top later.
Brush the pastry all over with remaining olive oil.
Add half of the filling mixture to the baking pan and spread evenly over the bottom crust.
Place the hard-boiled eggs horizontally onto the filling.
Add the remaining ricotta mixture then spread it evenly over the eggs.
Sprinkle grated parmigiano all over.
Completely cover the top of the ricotta layer with the smaller sheet. Press it to adhere to the side crust (you can roll on it the hanging parts from the side, crimping with your fingers).
Gently press the edge with a fork to create a pretty top edge.
Brush the top of the cake with olive oil.
Bake the cake in the oven until the top crust is golden, about 45 minutes.