Preheat oven to 350 degrees F.
In a large mixing bowl, add the light brown sugar, granulated sugar, cornstarch, pumpkin pie spice, cinnamon, and salt, and mix well until no clumps remain.
Add the pumpkin puree, coconut cream, vegan milk, and vanilla extract and gently whisk to combine. (Do not use a mixer or blender, or bubbles will form over the surface of the pie.) If there are any visible specks of coconut cream or cornstarch in the mixture, pinch with your fingers or remove them, otherwise they’ll show up in the pie.
Pour the filling into the prepared or par-baked crust and smooth over the surface to pop any bubbles before baking.
Place the pie on a baking sheet for easier handling. Then transfer it to the oven and bake for 60–75 minutes, or until there’s only a bit of jiggle left in the very center of the pie. Check at the 40-minute mark and tent the pie with foil if the edges are getting too dark. If the pie is still jiggly at 75 minutes, that's okay, it will firm up in the fridge!
Turn the oven off, but keep the pie in the oven. Crack the oven door several inches (or open it all the way if it won’t stay cracked), and allow the pie to cool this way for at least an hour before transferring to a cooling rack. Once completely cooled, transfer the pie to the fridge to finish setting for at least 4 hours or ideally overnight.
Remove the pie from the fridge 15 minutes before serving for a slightly chilled pie, or at least 1 hour prior to serving for room temperature.
Serve with whipped cream, if desired. Store leftover pie in the refrigerator.