In a medium saucepan, combine whole milk and double cream. Split a vanilla bean pod in half and scrape the seeds into the pot; add both the seeds and pod. Warm the mixture over medium heat until steaming, about 5-7 minutes.

In a large mixing bowl, whisk together egg yolks and granulated sugar until thick and pale, about 2-3 minutes.

Slowly pour the warm milk mixture into the egg mixture, whisking continuously for about 2 minutes to prevent cooking the eggs.

Return the combined mixture to the saucepan and heat over low, stirring constantly until thickened, about 8-10 minutes.

Strain the custard through a fine mesh sieve into a bowl, cover with plastic wrap, and refrigerate until chilled, preferably for at least 3 hours.

For the caramel brittle, heat the remaining granulated sugar in a saucepan over medium heat until melted and deep amber, about 5-7 minutes. Pour onto a parchment-lined tray to cool and harden, then chop into pieces.

Once the custard is chilled, churn it in an ice cream machine according to the manufacturer’s instructions, about 25-30 minutes.

Gently fold in ¾ of the caramel brittle pieces. Transfer to a freezer-safe container, topping with remaining brittle, cover tightly, and freeze for at least 6 hours.