Preheat the oven to 375°F. Remove the pie crust from the refrigerator and set aside.
In a medium saucepan, combine 2 cups of the huckleberries, the diced strawberries, 3/4 cup sugar, and 2 tablespoons lemon juice. Cook over medium heat for 8 to 10 minutes until the berries burst and the mixture thickens to a loose jam consistency. Mash it lightly with a spoon.
Remove the pan from heat. Stir in the remaining 2 cups of raw huckleberries, 1/4 cup cornstarch, and 1 teaspoon vanilla. Let it cool slightly while you make the crumble.
In a large bowl, whisk together 1.5 cups all-purpose flour, 1/2 cup sugar, 1.5 teaspoons baking powder, 1/4 teaspoon salt, and the zest of one lemon. Cut in 1/2 cup cold butter (cubed) until the mixture looks like coarse meal with some pea-sized butter bits remaining. Stir in 1/4 cup heavy cream and 1 teaspoon vanilla until just combined. It should look shaggy and clumpy — not like a smooth dough.
Pour the berry filling into the unbaked pie crust. Sprinkle the shortcake crumble evenly over the top. Don't press it down — leave those clumps.
Place the pie on a baking sheet. Bake for 45 to 55 minutes, until the crumble is deep golden brown and the filling is bubbling thickly around the edges. If the crumble is browning too fast at the 30-minute mark, tent it loosely with foil.
Let the pie cool on a wire rack for at least 2 hours. The filling needs to set so it slices cleanly. If you cut into it warm, it will run everywhere.