Preheat the oven to 350 degrees F.
Halve the squash and scrape out the seeds. Place the squash cut-side down in a roasting pan. Add 2 to 3 inches of water and roast the squash until it is very tender, about 30 minutes. Allow the squash to cool completely then mash or puree it in a food processor or blender. Measure 2 cups of the puree and reserve.
Combine the milk and sugar in a saucepan. Scrape the seeds from the vanilla bean into the milk then bring it to a simmer over medium heat.
Meanwhile, beat the egg yolks in a large bowl. When the milk reaches a simmer, temper the eggs by gradually whisking 1/2 cup of the hot milk mixture into the yolks. Repeat until half the milk is incorporated, then whisk in the remaining milk. Stir the reserved squash puree into the ice cream base then strain the base through a fine sieve into a bowl set over an ice bath.
Chill the ice cream base completely then process it in an ice cream maker according to the manufacturer's instructions. Spoon the ice cream into containers and freeze until firm. Serve the ice cream topped with spiced pumpkin seeds.
Preheat the oven to 350 degrees F.
Beat the egg white in a medium bowl until frothy. Add the pumpkin seeds, sugar, cinnamon, ginger, and nutmeg. Stir until the seeds are well coated.
Line a baking sheet with parchment paper. Spread the seeds on the baking sheet in a single layer. Bake the seeds, stirring occasionally, until they are golden. Remove the seeds from the oven and set them aside to cool.
