To Make the Crust: In a large bowl, combine flour, sugar, and salt. Add butter. Using your fingers or a pastry blender, combine until mixture resembles coarse pea-sized crumbles. Add water, a little at a time, and incorporate into dough just until it holds together. Alternatively, you can do this all in a food processor or stand mixer. The dough should hold together but still be a little flaky.
2. Divide dough into two even sections. Wrap each in plastic and shape into a disc. Refrigerate for at least an hour.
To Make the Filling:
1. Combine rhubarb with ¾ cup sugar. Let sit while you make the custard.
2. Using a stand mixer, beat together eggs, ½ cup sugar, salt, and flour until mixture is creamy and coats the back of a wooden spoon. Pour custard onto rhubarb and mix well.
To Assemble the Pie:
1. Preheat oven to 400F
2. On a lightly floured surface, roll out one of the discs of dough to fit the bottom of a 9 inch pie pan, allowing about ½ an inch of dough to hang over the edges. Roll out the second disc to similar size.
3. Insert the bottom crust into the pie pan. Pour in rhubarb custard and spread evenly. Add the top crust, trimming and then pinching around the edges. Cut several slits into the top crust to let steam escape while baking.
4. Bake for 50 minutes, until crust is golden brown. Remove from oven and let cool completely before serving.