In a medium saucepan, whisk together the cocoa powder and sugar. Slowly add the milk and heavy cream, whisking to combine.
Heat the mixture over medium heat until hot but not boiling, stirring occasionally.
In a separate bowl, whisk the egg yolks until smooth. Gradually pour about 1 cup of the hot chocolate mixture into the yolks, whisking constantly to temper the eggs.
Pour the egg yolk mixture back into the saucepan. Cook over low heat, stirring constantly, until the mixture thickens enough to coat the back of a spoon.
Remove from heat, stir in salt and vanilla extract. Let cool completely, then refrigerate for at least 4 hours.
Churn the chilled mixture in an ice cream maker according to the manufacturer's instructions until it reaches soft-serve consistency.
Transfer ice cream to a container and freeze until firm, about 2 hours. Serve and enjoy!
Notes
For an extra rich flavor, try adding chocolate chips or a swirl of fudge sauce before freezing.