In another bowl, add the flour and salt, and place the cubes of butter on top. Blend with your fingertips until mixture becomes flaky. Make a hole in the center of the mixture and gradually pour the liquid into it. Knead with the palms of your hands until the dough is smooth.
Cover with plastic wrap and place in the refrigerator for at least 1 hour.
Roll out the dough with a rolling pin. Place into a round baking dish with removable bottom and use a fork to poke holes in the dough.
Set aside in the refrigerator while making the filling.
Heat a skillet, add olive oil and brown the onions and garlic. Add the spinach, stir-frying for approximately 2 minutes. Remove from heat and set aside.
In a bowl, beat the eggs with a pinch of salt and pepper. Add the heavy cream, ricotta and spinach.
Spread the filling over the dough and top with the grated Parmesan cheese.
Place in the oven at 350°F for 40 minutes or until golden.