Place the egg yolks and ¾ cup of the sugar into a small mixing bowl. Beat on medium speed until the eggs and sugar are blended, thick and pale yellow in color, about 1 to 2 minutes.
Pour 1-½ cups of the milk into the top of a double boiler with the remaining sugar. Cook over medium heat, stirring frequently to dissolve the sugar. Heat until the milk is steaming and is about 175 to 180-degrees, about 10 minutes.
Add half of the hot milk to the egg yolks and sugar, about ½ cup at a time, whisking as you add the milk to keep the eggs from scrambling.
Return the eggs to the top of the double boiler and continue cooking over medium heat. Cook until the custard base starts to thicken slightly and the foam has cooked down, about 30 minutes. Stir frequently.
Place the pumpkin purée, the remaining milk, cream, cinnamon, ginger, and allspice into a large mixing bowl and whisk to blend together.
Whisk the custard base into the pumpkin mixture.
Pour the custard base into a heatproof container, place a piece of plastic wrap directly on top of the custard, cover the container and refrigerate until well chilled, about 6 hours or overnight.
When you’re ready to make the ice cream, pour the chilled custard into your ice cream machine and churn until the ice cream has just set up, about -22 degrees.
Transfer the ice cream to a freezer proof container and freeze until the ice cream has set up.