In a large bowl, use a silicone spatula to toss rhubarb and strawberries with sugar to evenly coat. Set aside to macerate for 1 hour.

In a small bowl, whisk cornstarch, pectin, and salt to combine; set aside.

Meanwhile, Shape Pie Crust: Place pie dough on a well-floured surface. Using a rolling pin, roll 1 disc of pie dough into a circle roughly 14 inches in diameter. Transfer pie dough to a 9-inch pie plate, lightly cover with plastic wrap, and refrigerate until ready to use.

For a Solid-Top Pie: Roll remaining dough as before; place dough on a rimmed baking sheet lined with parchment paper. Lightly cover with plastic wrap, and refrigerate until ready to use.

For a Lattice-Top Pie: Roll remaining dough into a 9- by 15-inch rectangle. Using a pizza cutter, fluted pastry wheel, or knife, cut dough into a dozen 10-inch strips, each about 1-inch wide. Set dough strips on a rimmed baking sheet lined with parchment paper, lightly cover with plastic wrap, and refrigerate until ready to use.

In a large bowl, set up an ice bath by partially filling it with a combination of cold water and ice. Set aside.

In a large pot, combine rhubarb/strawberry mixture with vanilla paste and cornstarch mixture. Cook over medium heat, stirring often, until fruit softens slightly and until mixture just thickens, about 2 minutes of simmering. Remove from heat. Scrape fruit filling to a large bowl; set bowl over prepared ice bath. Let sit until room temperature, about 30 minutes.

Adjust oven rack to lowest position and preheat oven to 410°F convection.

Scrape filling into prepared pie shell and top with pie dough or weave strips into a lattice . Using a pair of kitchen scissors, trim edges of both pie crusts until they overhang the edge of the pie plate by ½ inch all the way around. Using a pair of kitchen scissors, trim edges of both pie crusts until they overhang the edge of the pie plate by ½ inch all the way around. Fold edges of both pie crusts down together, tucking them in between the bottom crust and the pie plate and working your way all the way around the pie until everything is tucked. Use the forefinger on your left hand and the thumb and forefinger on your right hand to crimp the edges. If using a solid top crust, cut 5 slits in the top with a sharp paring knife for ventilation.

Bake until the juices are bubbling and the crust is golden brown, 45 to 55 minutes, or until internal temperature is 175-185 degrees. Remove from oven, transfer to a cooling rack, and allow pie to cool completely before serving, about 4 hours.