Combine 1 cup 1% milk and brown sugar in a medium, heavy saucepan, and heat to 180° or until tiny bubbles form around edge (do not boil). Remove from heat.
Place egg yolks in a bowl. Gradually add hot milk mixture to egg yolks, stirring constantly with a whisk. Place mixture in pan. Cook over medium heat until mixture coats a metal spoon (about 4 minutes), stirring constantly. Drain custard through a sieve into a bowl; discard solids.
Combine 1/2 cup 1% milk, sweetened condensed milk, and next 5 ingredients (sweetened condensed milk through salt) in a medium bowl. Stir in pumpkin. Gradually add custard, stirring with a whisk. Cover and chill at least 8 hours.
Combine 1/2 cup pumpkin mixture and sour cream, stirring well with a whisk. Add sour cream mixture to chilled pumpkin mixture, and stir until well blended. Pour the mixture into freezer can of an ice-cream freezer, and freeze according to manufacturer's instructions.
Spoon ice cream into a freezer-safe container; fold in crumbled biscotti. Cover and freeze 1 hour or until firm.