Thaw frozen spinach in the microwave on defrost (spinach must still be raw.) Let the spinach drain in a colander in the sink.
While spinach is draining, prepare dough. In a large mixing bowl, use a pastry cutter to cut the butter into the flour until coarse crumbs appear.
In a small bowl, use a fork to beat the liquids together (5 tablespoons water, egg white & vinegar). Add a little of the liquid mixture to the dry ingredients and stir with a fork. Continue adding a little bit of liquid at a time and mixing. Press the butter into the flour with the fork. Add an extra tablespoon of water if needed.
Gather the dough into a ball and wrap it in plastic. Refrigerate the dough for 15 minutes and preheat the oven to 375 degrees.
While the dough is chilling, chop the onion, garlic, and parsley and grate the Pecorino Romano and Parmesan. Set them aside and prep the counter for rolling out the dough. (You can use a floured pastry cloth or parchment paper.) Place a 9x13 glass pan face-down on the surface and sprinkle flour in a rectangular frame around it, two inches beyond the pan's edges. This will be the outline to guide your rolling.
Set aside the pan and place the dough in the center of the flour rectangle. Using a floured rolling pin (or a cloth-covered rolling pin), firmly roll the pastry out into a rectangle that fits into your outline (press down, roll, and lift as you go.) If the dough separates at the edges, just push it back together with your fingertips and roll over it to smooth it out. When the pastry is smooth and the right size, transfer it to the ungreased pan. (You can lift your cloth or parchment paper and turn the dough into the pan.) Trim any dough that overhangs too far. If the dough is thin at the edges, you can fold the edges inside the rim of the pan before crimping them with your fingertips. If the dough is thick at the edges, just flute it without folding it under. Brush cold water on the edges of the pan so the crust will stick to the rim and not slide down. Refrigerate the pan with the raw crust while you finish the filling.
Dry the spinach with paper towels and squeeze out any excess liquid. Melt the butter (and olive oil if using fresh spinach) in a pan on the stove. Add the onions and garlic and cook for 2-3 minutes on low heat. Then add the spinach to the pan, sprinkling with salt and black pepper. Stir and cook on medium for 3-4 minutes. Off the heat, stir Romano into the pan.
Place the spinach mixture in a large mixing bowl. Add the ricotta and parsley and stir well until blended. Fold in the beaten eggs. Pour the filling into the pan of raw crust. Sprinkle Parmesan on top. Place pan on the bottom rack of the oven. Bake uncovered, for 1 hour, or until the surface is golden brown. Let cool for a few minutes before cutting.
If using unsalted butter, you will need to add an extra ¼ teaspoon salt to the filling and 1 teaspoon salt to the crust.Please note that Mom's Spinach-Ricotta Pie should not be reheated in the microwave, because it will ruin the texture and flavor. You can either take leftovers out of the refrigerator and let them come to room temperature, or reheat the pie in the oven at 350 degrees, uncovered. Start with 15 minutes and see if it needs more time.