Step 1

Fold 1 dough round in half and carefully transfer to a 9-inch (23-cm) pie dish. Unfold and ease the round into the pan, without stretching it, and pat it firmly into the bottom and up the sides of the dish. Using kitchen scissors, trim the edge of the dough, leaving 3/4 inch (2 cm) of overhang and reserving any dough scraps. Set the dough-lined pan aside, along with the second dough round, in a cool place until ready to use.

Step 2

In a small bowl, stir together the sugar, cornstarch, tapioca and salt. Place the strawberries and rhubarb in a large bowl, sprinkle with the sugar mixture and toss to distribute evenly. Immediately transfer to the dough-lined pan. Dot with the butter.

Step 3

Place a lattice pie crust cutter on your work surface and arrange the remaining dough round on top. Using a rolling pin, press the dough into the lattice cutter. Lift off the insert and the dough from the lattice cutter, then invert the dough over the pie and lift the insert. Fold the edge of the top round under the edge of the bottom round and crimp the edges to seal. Brush the crust with the egg wash.

Step 4

Refrigerate the pie until the dough is firm, 20 to 30 minutes. Meanwhile, position a rack in the lower third of an oven and preheat to 350°F (180°C).

Step 5

Bake the pie until the crust is golden and the filling is thick and bubbling, 50 to 60 minutes. If the lattice begins to get too dark, tent with aluminum foil for the remainder of the cooking time.

Step 6

Transfer to a wire rack and let cool completely to set. Serve at room temperature or rewarm in a 350°F (180°C) oven for 10 to 15 minutes just before serving.

Step 7

Adapted from Williams-Sonoma Collection Series, Pie & Tart, by Carolyn Beth Weil (Simon & Schuster, 2003)