Mix the base: In a small bowl, whisk cocoa powder and boiling water until a smooth paste forms with no lumps. Add cream and milk, whisking until well combined. Add condensed milk, vanilla, and salt. Whisk thoroughly until completely smooth.
Freeze: Pour mixture into Cuisinart dessert tub up to the max fill line. Cover with lid and freeze until completely solid, at least 8 hours or overnight.
Churn with Freeze Wand: Remove tub from freezer and let stand at room temperature for 5 minutes to soften slightly. Insert Freeze Wand and churn 2-3 times. Remove wand and check texture, scraping sides and bottom to ensure no solid chunks remain. Spin again if needed until smooth and creamy.
Add mix-ins: Turn wand handle to mix-in function. Add chopped hazelnuts and run through one cycle to incorporate evenly.
Serve: Serve immediately