Whisk the coconut cream, oat milk, sugar, cocoa powder, corn syrup, cornstarch, and sea salt in a saucepan until smooth.
Cook the base over medium heat for 5 to 7 minutes, whisking constantly, until slightly thickened. Stir in the chocolate hazelnut spread and vanilla extract.
Refrigerate the chocolate base in a covered container for at least 4 hours, until completely cold.
Stir the melted dairy free chocolate with coconut oil, then toss in the chopped hazelnuts until coated. Spread the hazelnuts on parchment paper and refrigerate until crisp.
Break the chocolate hazelnut crunch into small pieces once set.
Churn the cold ice cream base in an ice cream maker until thick and creamy.
Fold in the brownie pieces and half of the hazelnut crunch, then transfer the ice cream to a freezer-safe container.
Scatter the remaining hazelnut crunch over the top, cover with parchment paper, and freeze for 4 hours.