Have an ice bath ready before making the gelato. This will help to quickly cool down the custard.
Pour the milk, 1 cup of the heavy cream, 1/3 cup of the sugar, the corn syrup, maple syrup, molasses, grated ginger, cinnamon, ground ginger, nutmeg, salt and vanilla bean and seeds into a medium, heavy-bottomed saucepan and stir to combine. Place over medium heat, stirring occasionally, until warm.
In a stainless or glass bowl, whisk together the remaining 1/3 cup of the sugar and the egg yolks until slightly thickened. Temper the sugar and yolk mixture with some of the spiced hot milk. While quickly whisking, slowly drizzle some of the hot milk into the yolks.
Pour the warm egg mixture back into the saucepan. Clip on a candy thermometer or instant-read thermometer. Stirring continuously with a rubber spatula, cook the mixture over medium heat until it reaches 170 degrees F. Do not allow this to boil or you will have scrambled eggs!
Pour the hot gelato base through a fine mesh sieve into a bowl. Add the remaining 1 cup cold heavy cream, the pumpkin puree and whisk until completely mixed.
Plunge the container of gelato into a bowl filled with ice water. The ice water should come up to the level of the gelato. Stir the gelato until cool, especially the very center.
Once cool, cover with plastic wrap and chill overnight. This recipe can be frozen once cool, but will taste much better if allowed to chill overnight or at least 8 hours.
To freeze, pour the cold gelato into the ice cream maker and process according to the manufacturer's instructions. While the gelato churns, place the chopped chocolate in a small, dry stainless steel bowl. Set aside.
Bring a small saucepan of water to boil over a high heat. Once boiling remove from the stove. Place the small bowl of chopped chocolate over the hot water stirring often until completely melted. The chocolate should be warm not hot. Dry the bottom of the bowl as not to get the water into the gelato.
Drizzle the melted chocolate into the ice cream machine in the last few minutes of freezing. As soon as the warm chocolate hits the cold gelato, instant chocolate shards happen. It's like magic.
This can be served immediately or for a firmer gelato, freeze in a covered container until firm.