Stir the flour and 1/2 tsp salt together in a bowl. Add the water and 3 tbsp olive oil, then knead on the counter for 8 minutes until smooth and elastic. Divide into one piece of about 330 g and one of about 160 g, cover, and rest for 30 minutes while you make the filling.

Slice the chard stems 1 cm thick and roughly chop the leaves. Roughly chop the spinach.

Warm 2 tbsp olive oil in a 5-quart / 4.7 L pot over medium heat. Cook the onion for 4 minutes until soft and pale. Add the chard stems and cook 3 minutes, then add the chard leaves and spinach in handfuls and cook 5 minutes until collapsed and tender.

Tip the greens into a colander and cool for 15 minutes. Squeeze them hard in a clean kitchen towel until almost no liquid drips out. You should have about 300 to 350 g. Chop them finely.

Mix the ricotta, Parmigiano, eggs, marjoram, nutmeg, 3/4 tsp salt and pepper in a large bowl. Fold in the greens until evenly combined.

Heat the oven to 190 C / 375 F with a rack in the lower third. Brush a 24 cm / 9.5-inch tart pan with 1 tbsp olive oil. Roll the larger piece of dough to a 34 cm round about 3 mm thick, drape it into the pan, press into the corners and leave the overhang.

Spoon in the filling and smooth the top. Roll the smaller piece to a 26 cm round, lay it over the filling, then fold the bottom overhang over the edge and crimp with your fingers. Prick the top 6 to 8 times with a fork and brush with 1 tbsp olive oil.

Set the pan on a 33 x 46 cm / 13 x 18-inch sheet pan and bake for 45 minutes, until the top is deep gold, the edges are crisp and the filling feels set when pressed.

Cool on a rack for 20 minutes. Unmold, cut into 8 wedges and serve warm or at room temperature.