Add the flour and salt to the bowl of a stand mixer. Gradually add the remaining dough ingredients while mixing. Once the dough comes together and forms a ball, remove it from the hook so it doesn't stick. Sprinkle a little flour on top and let it rest for 1 hour.

For the filling: Finely chop the onion and sauté it in a little olive oil. Add the spinach. Once the spinach has wilted and reduced, add salt and pepper. Turn off the heat and transfer the mixture to a colander to drain well. Press it lightly once it cools. Place the filling in a bowl, add the eggs, and mix well.

Divide the dough into 8 equal pieces. Roll each piece into a thin sheet. Grease a small baking pan and lay down 4 sheets, brushing each with olive oil as you layer. Sprinkle the breadcrumbs over the bottom sheets, then add the spinach filling. Cover with the remaining 4 sheets, brushing each with olive oil. Fold any overhanging dough over the edges of the pan and brush with more olive oil. Sprinkle a little water over the top with your hand. Score the pie and bake at 350°F (180°C) for about 45 minutes.