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1
In a large bowl, whisk together the flour, sugar, and salt.
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2
Toss the shortening and butter in the flour mixture until well coated.
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3
Using a pastry blender or 2 knives, cut the shortening and butter into the dry ingredients until reduced to pea-size pieces, about 3 to 4 minutes.
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4
Add the sour cream and mix just until the dough comes together, being careful not to work the dough too much.
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5
Divide the dough into 2 flat disks, one slightly larger than the other.
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6
Wrap tightly in plastic wrap and refrigerate for at least 1 hour.
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7
Remove the dough from the refrigerator and set it aside at room temperature for 30 minutes.
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8
On a lightly floured surface, roll out the slightly larger disk to about 12 inches in diameter and 1/4 inch thick.
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9
(If the dough is very crumbly, gather it into a ball and knead it a few times to make it more pliable, then roll it out.)
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10
Line a 9-inch pie plate with the dough and trim it to leave a 1-inch overhang.
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11
Set aside.
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12
Place 1 teaspoon of the sugar in a small bowl and set it aside.
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13
Place the remaining sugar and cornstarch in a large bowl and whisk to combine.
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14
Sprinkle 2 tablespoons of the sugar-cornstarch mixture evenly over the bottom of the pie crust.
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15
Add the rhubarb, strawberries, and lemon juice to the bowl with the remaining sugar-cornstarch mixture and stir to evenly coat the fruit.
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16
Set aside.
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17
Roll out the remaining dough disk on a lightly floured surface to about 11 inches in diameter and 1/4 inch thick.
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18
Using a 1-inch round cutter, stamp out circles, leaving at least a 3-inch border from the edge and 1 1/2 inches of space between each circle (you should have about 12 cutouts).
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19
Set the cutout circles aside.
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20
Stir the rhubarb-strawberry mixture to redistribute the juices.
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21
Pour it into the prepared crust, mounding it in the center, and gently pat it down.
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22
Brush the dough overhang with the egg white.
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23
Place the top crust over the fruit and trim the excess dough to a 1-inch overhang.
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24
Fold the edge of the bottom crust over the top crust and press to seal.
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25
If desired, crimp the edge, using the forefinger of one hand to push the dough between the forefinger and thumb of the other hand.
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26
Brush the top of the pie with some of the remaining egg white.
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27
Arrange the cutout circles intermittently over the top crust (not covering the holes), and brush the cutout circles with egg white, discarding any left over.
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28
Evenly sprinkle the reserved sugar over the top of the pie.
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29
Place the pie in the freezer while the oven heats.
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30
Heat the oven to 425 degrees F and arrange a rack on the bottom.
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31
Place a baking sheet lined with a double layer of aluminum foil on the rack.
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32
Place the pie on the hot baking sheet and bake for 30 minutes.
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33
Lower the temperature to 350 degrees F and bake until the crust is brown and the fruit is bubbling, about 1 hour 40 minutes more.
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34
(The center of the filling should read 212 degrees F on an instant-read thermometer for it to set properly.)
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35
If the crust around the edges of the pie starts to brown before the pie is done, cover the edges with aluminum foil.
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36
Remove the pie from the oven and let it sit on the baking sheet until the fruit stops bubbling, about 5 minutes.
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37
Transfer to a wire rack to cool completely and let the filling set before slicing, at least 3 hours.
