Pre-heat oven to 350F. For Crust: In a mixer, mix the flour and salt. Add the butter in two batches. When the flour is a mealy texture, slowly add the water. You may not need to add all of the water depending on what time of the year it is based on the humidity that is present or not. The dough is done when it releases from the side of the mixing bowl.
Form the dough into a disc and wrap in plastic. Refrigerate for at least an hour. (Can be made a week ahead). Roll the dough out on a floured surface to about 1/8 inch thickness. Fold in half to easier carry and place in the cake pan.
Press the dough into the corners and press firmly on the sides to keep it there. Place in the freezer for about ten minutes. Make the filling while shell is in the freezer.
For Filling: Saute the onions over medium-high heat with a little olive oil. Remove from the heat when golden. Place the eggs in a mixing bowl and mix on medium speed. Add the cream, herbs, salt and pepper. Pour the egg mixture into the prepared shell. Evenly place the onions and feta in the filling and place in the oven. It will take about 60 minutes. Set a timer for 15 minute intervals to rotate the pie to ensure even browning. Turn the temperature down if browning to fast.
Remove from the oven when there is almost no jiggling in the center. Let cool for about 15 minutes and run a paring knife around the edges to release the dough from the sides. Remove the cake ring and slice to serve.