In a medium saucepan, warm the milk over medium heat until it just starts to bubble around the edge (no need to bring it to a boil). Remove from the heat and reserve.
In the bowl of a stand mixer, or in a large mixing bowl if you’re using a hand mixer, beat the egg yolks and sugar together until the mixture is thick and creamy (about 2 minutes at medium speed). With the mixer on low speed, slowly pour in one ladleful of the hot milk into the egg mixture. Slowly pour in the rest of the mixture and beat until the milk is well incorporated.
Pour the milk and egg mixture back into the saucepan, add the vanilla bean, and place over medium-low heat and cook, stirring constantly, until the custard coats the back of a wooden spoon.
Remove from the heat. Let cool to room temperature, then refrigerate for a few hours, or preferably overnight to infuse the custard with a deeper vanilla flavor.
Fish the vanilla bean out of the custard, then pour the custard through a fine mesh strainer into the bowl of an ice cream maker (straining the mixture will ensure a silky smooth gelato). Freeze according to the manufacturer’s instructions. Stop the machine when the gelato is icy but still soft.
STORAGE: Transfer the gelato to an airtight container and freeze until firm, about two hours.Classic gelato is at its creamiest and best if enjoyed within 2 weeks. Past that, some ice crystals will inevitably start forming (especially if the gelato is kept in the freezer section of a regular fridge, as opposed to a chest freezer) and the texture won't be quite as smooth. The gelato will still be perfectly edible for up to 2 months, but my advice is: enjoy it as quickly as possible after churning.Always take gelato out to room temperature 15 to 20 minutes before serving to soften it and make it easier to scoop.
SERVING: Always take Gianduja gelato out to room temperature 20 minutes before serving to make it easier to scoop. This will also allow you to enjoy the treat at its ideal temperature and texture.
MAKE IT DAIRY FREE: Substitute lactose-free milk or oat milk for the regular milk, and lactose-free heavy cream or soy cream for the regular heavy cream.