Whisk together the sugar, cornstarch, salt, and vanilla bean in a large saucepan.

Gradually add the milk and cream. Cook the mixture over medium to medium high heat for about 10 to 15 minutes or until the mixture comes to a bubble. It will have thickened and be like a loose pudding.

In another bowl, whisk the egg yolk and vanilla extract if you are using it.

Very, very slowly pour the cream mixture over the egg yolk. Whisk well.

Pour the mixture through a sieve or a strainer. Cover and chill the mixture for 8 hours or overnight.

Pour the chilled mixture into your ice cream maker. Freeze according to the machine’s instructions. Add the marshmallows and white chocolate chips a few minutes before the ice cream is finished.

Pour the ice cream into a container and continue to freeze in the freezer.

Scoop the ice cream into cones or a bowl.