Spray a 9-inch pie plate with a light coating of cooking spray. Sprinkle about 1 teaspoon of the wafer crumbs, if using, on the bottom of the pie plate.
Roll out 1 sheet of the pie dough until large enough to fit into your prepared pie plate with 1 inch of overhang all around. Press the dough into the pie plate. Sprinkle the remaining wafer crumbs on top of the pie crust and refrigerate. Roll out the remaining sheet of pie dough into a rough rectangle about 1/8 inch thick and refrigerate while you prepare the filling.
Combine the cherries and strawberries in a large bowl. Mix the sugar, cornstarch, salt and lemon zest in a small bowl. Sprinkle over the fruit and mix well. Add the lemon juice and vanilla and toss to coat. Pour the filling into the chilled bottom crust. Brush some of the heavy cream onto the edge of the overhanging dough.
Remove the rectangle of dough from the refrigerator and cut into 1-inch-wide strips. Lay strips of dough across the entire pie in one direction about 1 inch apart. Starting at one end of the pie, fold back every other strip halfway. Lay another dough strip perpendicular to the first row of strips. Unfold the strips back over the new strip, then fold alternate strips back halfway. Add another perpendicular strip; unfold the strips back over it. Repeat to form a lattice. Trim off excess dough from the strips and then fold in the 1 inch overhang, rolling it in towards the edge of the pie plate so that it sits on top of the plate's rim. Crimp as desired.
Brush just the lattice portion with the remaining heavy cream. Place the pie in the freezer for 30 minutes to chill and rest.
Place a foil-lined rimmed baking sheet on the center rack of the oven and preheat to 400 degrees F. When the pie has chilled, place it on the preheated baking sheet and bake until the crust is golden and the pie is bubbling vigorously, 65 to 75 minutes, checking the pie after 35 minutes for browning. Rotate the baking sheet back to front. If the pie is browning too quickly, take a piece of aluminum foil, poke a few holes in it, then lay it gently over the top of the pie for the remainder of the bake time. The center of the pie must be bubbling for the cornstarch to be fully activated. The center of the pie should reach an internal temperature of about 212 degrees F.
Let cool for at least 3 hours before serving to allow the filling to thicken.
Sprinkling wafer crumbs on the pie plate and pie crust ensures a crisp and well baked bottom crust. This step is optional but recommended.