Add 3/4 cup chopped dark chocolate to a pot on the stove set to low heat (reserve the remaining chocolate for later).
Cook, stirring often, until the chocolate is completely melted and no solid lumps remain, then immediately remove the pot from the heat.
Transfer the melted chocolate to a bowl, then add the pumpkin puree and pumpkin pie spice and stir to combine.
Refrigerate the chocolate pumpkin mixture for 30 minutes.
When the chocolate pumpkin mixture has finished chilling, mix it well then leave it at room temperature for 5 minutes.
Scoop out one tablespoon of the pumpkin chocolate mixture and use your hands to roll it into a ball (wearing kitchen gloves makes this easier), then place it on a plate lined with parchment paper or a silicone baking mat. Repeat with the rest of the pumpkin chocolate mixture (you should end up with twelve balls).
Add the remaining 3/4 cup chopped dark chocolate to a pot on the stove set to low heat, then stir until melted.
Once the chocolate has melted, immediately remove the pot from the heat and transfer the melted chocolate to a bowl.
Add a pumpkin chocolate ball to the bowl of melted chocolate, then gently stir to coat it completely.
Use a fork to lift the pumpkin chocolate ball out of the bowl of melted chocolate and place it on the plate lined with parchment paper or a silicone baking mat.
Add a sprinkle of pumpkin pie spice on top of the chocolates, if desired, then repeat with the rest of the pumpkin chocolate balls.
Place the plate of truffles in the fridge to harden for at least one hour before serving.