Preheat the oven to 400 degrees F (200 degrees C). Arrange one of the 9-inch Pie Crust (2) in the bottom of a pie pan, pressing the bottom and sides of the crust. Set aside.
In a large bowl, combine the Rhubarb (1.5 pound), Fresh Strawberry (1.3 pound), Brown Sugar (1/4 cup), Granulated Sugar (1/4 cup), Arrowroot Starch (1/4 cup), Salt (1/4 teaspoon), and Lemon Juice (1 tablespoon), Lemon (1). Toss to combine.
Transfer the berries and rhubarb to the pie shell, leaving any excess liquid in the bottom of the bowl and spread evenly into the crust.
Cut the remaining crust into 1 inch strips.
Weave a lattice crust, then tuck any loose ends underneath the overhang of the bottom crust and pinch the edges into a decorative border. Brush the crust with the Heavy Cream (2 tablespoon) and sprinkle with Demerara Sugar (2 tablespoon).
Place the pie on a baking sheet covered with aluminum foil to catch any spills. Bake for 20 minutes at 400 degrees F (200 degrees C).
Turn the oven down to 350 degrees F (180 degrees C) and bake for an additional 25-30 minutes. Remove from oven and let cool to room temperature. Serve.