Preheat the oven to 400°F.
Combine pumpkin puree, egg, maple syrup, 3tbsp of the melted butter, cream cheese, vanilla, salt and pumpkin spice mix in a mixing bowl. Beat well until smooth, 2~3 minutes. Set aside.
Unwrap the dough on a parchment. Cover with another parchment and roll into a 12" round that is 1/8" thick.
Slide the dough along with the parchment onto the baking sheet. Remove the top parchment.
Spoon the pumpkin filling onto the center of the dough, leaving a 2" border around the edge. Fold the rim of the dough up and over the filling, overlapping the dough and pleat it as you go.
Brush the crust with 1tbsp melted butter and sprinkle generously with coarse sugar, if desired.
Bake the galette until the crust is golden brown, about 30~35 minutes. Transfer the galette onto a wire rack to cool completely.