With the food processor running, pour the liquid through the feed tube and process about 30 seconds, until a soft dough forms and gathers on the blade. If the dough is not coming together, add a little more water in small amounts until you have a smooth, soft dough.
You can also make this dough by hand in a bowl using a fork to bring the ingredients together.
Turn the dough onto a lightly floured board and knead for a minute until it’s smooth and soft. Wrap in plastic wrap and let rest at room temperature for 1/2 hour. You can refrigerate for up to a day. Let come to room temperature before rolling.
Bring water to boil in a large pot and add all the chard, submerging the strips. Boil for about 10 minutes, until the chard is tender. Drain and cool, then squeeze the leaves by hand, pressing out as much water as possible.
Pour the olive oil into a skillet and set it over medium heat. Stir in the chopped onion and cook until onion is softened. Add the drained chard, salt and mix to coat with the oil and cook for a few minutes. Transfer to a large bowl and cool briefly.
Add beaten eggs, some freshly grated nutmeg, the ricotta and Parmigiano-Reggiano cheeses, pine nuts and bread crumbs and mix. Set aside.
Preheat the oven to 375 degrees. Roll the dough out onto lightly floured work surface, gradually stretching it into a circle. Drape the sheet of dough over a parchment-lined baking sheet.
Spread the filling onto the dough-lined pan in an even layer and then fold the flaps over, with the filling exposed in the middle. Brush egg wash over crust.
Bake in the oven for about 30 minutes, until the crust is golden and the filling is crisp on top. Cool on a wire rack for 30 minutes.