Rhubarb pie balances the sharp tartness of fresh rhubarb with enough sugar to round it out, all baked inside a double-layer flaky crust. Plan for about 30 minutes of prep and 50 minutes of baking time; letting the pie cool fully before slicing helps the filling set cleanly.
To make the pie crust, combine the flour and salt in a bowl. Add the chilled butter, and use a pastry cutter or your fingertips to blend the butter into the flour until the mixture resembles coarse crumbs.
Drizzle the ice water into the flour mixture, stirring with a fork until the dough can be gathered into a ball. Divide in half, shape into disks, and wrap in plastic. Chill for at least 1 hour.
Preheat your oven to 400°F (204°C). Roll out one dough disk on a floured surface to fit a 9-inch pie dish. Drape the crust over the pie dish, and press it gently into the corners.
In a large bowl, combine rhubarb, sugar, and flour. Mix until rhubarb is evenly coated, then pour into the prepared crust. Dot with butter pieces.
Roll out the second dough disk for the top crust. After placing it over the filling, trim and crimp the edges. Cut small slits into the top to allow steam to escape.
Brush the crust with beaten egg for a glossy finish. Protect the crust edges with aluminum foil to prevent over-browning.
Bake in the preheated oven for about 50-60 minutes, or until the crust is golden and the filling is bubbling through the slits. Allow the pie to cool before serving.
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Notes
For a twist, try adding a teaspoon of vanilla extract to the filling or substituting a portion of the rhubarb with strawberries for a sweeter profile.
If you've got a short amount of time, you can prepare the dough a day ahead.
Leaving the pie to cool properly is key to letting the juices set up nicely.