Old-Fashioned Rhubarb Pie

From the garden

• 6 cups rhubarb stalks, leaves stripped, sliced 1/2 inch thick · about 2 pounds of trimmed stalks

From the pantry

• 2½ cups all-purpose flour · for the pastry, plus a little for rolling
• 1 cup butter, very cold, cut in 1/2 inch cubes · 2 sticks, for the pastry
• 1¼ cups granulated sugar · for the filling, plus 1 tablespoon for the top
• 3 tbsp cornstarch · rhubarb runs wetter than most fruit, so do not cut this back
• 1 egg, beaten with a splash of water · for the wash
• ¾ tsp salt

1. Whisk the flour and salt in a wide bowl, add the cold butter, and rub or cut it in until the pieces range from oat flakes to peas. Sprinkle in 6 to 8 tablespoons of ice water, tossing, until the dough holds when squeezed.
2. Divide the dough in two, one piece slightly larger, press each into a disk, wrap, and chill at least 1 hour. Cold, rested pastry rolls without fighting back and shrinks less in the oven.
3. Toss the sliced rhubarb with the 1.25 cups sugar and the cornstarch and let it stand 15 minutes while the oven heats to 425°F with a rack and a sheet pan in the lower third.
4. Roll the larger disk to a 12 inch round and line a 9 inch pie plate. Tip in the rhubarb and any syrup at the bottom of the bowl, mounding it slightly, since it settles as it bakes.
5. Roll the second disk, lay it over, trim to a 1 inch overhang, tuck under, and crimp. Cut four generous vents, brush with the egg wash, and scatter the remaining tablespoon of sugar over the top.
6. Bake on the hot sheet pan 20 minutes at 425°F, then drop to 375°F for 40 to 45 minutes, until the crust is deep gold and thick juice bubbles slowly through the vents. Tent the edges with foil if they darken early.
7. Cool on a rack at least 3 hours before cutting. A warm rhubarb pie runs; a cooled one slices, and a slice can always go back into a warm oven.