01 - In a medium saucepan, combine whole milk, heavy cream, and half the sugar. Warm over medium heat until steaming but not boiling.
02 - Add the chopped dark chocolate and cocoa powder to the saucepan. Whisk constantly until fully melted and smooth. Remove from heat.
03 - In a separate bowl, whisk the egg yolks with the remaining sugar until the mixture turns pale and slightly thickened.
04 - Slowly pour one cup of the hot chocolate mixture into the yolks while whisking constantly to temper. Then pour the tempered yolk mixture back into the saucepan.
05 - Return the pan to low heat and cook, stirring constantly, until the custard thickens enough to coat the back of a spoon (approximately 175°F).
06 - Remove from heat immediately and stir in the vanilla extract and fine sea salt until evenly distributed.
07 - Allow the custard to cool to room temperature, then whisk in the sourdough starter until fully incorporated and no streaks remain.
08 - Cover the surface directly with plastic wrap and refrigerate for at least 4 hours or until the mixture is thoroughly chilled.
09 - Pour the chilled mixture into an ice cream maker and churn according to the manufacturer's instructions, approximately 20–25 minutes, until it reaches a soft-serve consistency.
10 - Transfer the churned ice cream to a freezer-safe container, smooth the top, and freeze for at least 2 hours until firm enough to scoop.
11 - Scoop into bowls or cones and serve. Optionally garnish with a drizzle of chocolate sauce or a sprinkle of flaky sea salt.