Use a paring knife to split the vanilla bean down the middle. Then use the back of the knife to scrape the vanilla seeds out of each side.
Combine the vanilla, milk and cream in a saucepan and bring to a slow boil over medium heat stirring occasionally.
Meanwhile, separate the egg yolks and add them to a mixing bowl. Add the eggs and sugar and whisk well for about two minutes or until the mixture becomes pale.
When the vanilla, milk and cream mixture has come to boiling, remove the saucepan from the heat and discard the vanilla bean.
Take one cup of vanilla, milk and cream mixture and slowly pour it into the egg and sugar mixture in a steady steam, whisking constantly.
Pour the egg and sugar mixture back into the saucepan with the remaining vanilla, cream and milk. Whisk well to combine.
Return the saucepan to the stove and cook the custard over a medium-low heat stirring constantly with a wooden spoon until the mixture is thick enough to coat the back of the wooden spoon.
Transfer the custard into a bowl and add the vanilla extract. Mix well to combine.
Cover with plastic wrap directly on top of the custard. This helps to avoid a 'skin' forming as the custard cools. Leave to cool on the bench for about 1 hour.
Cover with another layer of plastic wrap on top of the bowl (to avoid unwanted flavours being absorbed into the custard) and place the custard to the fridge to chill overnight (or for at least 8 hours) and the custard is around 4°C (39.2°F).
Churn the ice cream. Ice cream maker method: Pour the mixture into the bowl of the ice cream maker, insert the whisk, attach the lid and begin churning. Churn for approximately 25 minutes, or until almost frozen. Then transfer the churned ice cream into a freezer-safe container. Hand churning method: Pour the chilled custard mixture into a freezer-safe container and place it in the freezer. After 45 minutes mix the ice cream with a wooden spoon, scraping down the sides of the container. Return to the freezer for another 45 minutes. Continue this process until almost frozen, for about 8 hours. Cover and freeze for at least 3 hours before serving.