In a medium saucepan, combine the frozen black currants and ½ cup of granulated sugar.
Cook over medium heat until the berries release their juices and begin to burst, stirring occasionally.
Once the mixture thickens slightly, remove from heat and let it cool completely.
Prepare the Ice Cream Base:
In a mixing bowl, whisk together the egg yolks and ½ cup of granulated sugar until the mixture becomes pale and thick.
In a saucepan, heat the whole milk over medium heat until it reaches approximately 165°F (74°C). Avoid boiling.
Gradually pour about ½ cup of the warm milk into the egg yolk mixture, whisking continuously to temper the eggs.
Pour the tempered egg mixture back into the saucepan with the remaining milk.
Cook over medium heat, stirring constantly, until the mixture thickens enough to coat the back of a spoon. This forms a custard base.
Remove from heat and let it cool slightly.
Combine and Chill:
In a large mixing bowl, combine the cooled custard base, heavy cream, the remaining ½ cup of granulated sugar, vanilla extract, and the cooled black currant syrup.
Whisk until thoroughly mixed.
Cover the mixture with plastic wrap, ensuring it touches the surface to prevent a skin from forming.
Refrigerate for at least 4 hours, or until the mixture is very cold.
Churn the Ice Cream:
If using an ice cream maker, ensure the bowl has been frozen according to the manufacturer's instructions (typically 15–24 hours).
Assemble the ice cream maker and turn it on before adding the mixture to prevent the bowl from freezing up.
Pour the chilled mixture into the running ice cream maker.
Churn according for 30–35 minutes, until the ice cream reaches a soft-serve consistency.
Freeze and Serve:
Transfer the churned ice cream into an airtight container.
Place a piece of plastic wrap directly on the surface of the ice cream to prevent ice crystals from forming.
Seal the container and freeze for at least 2 hours, or until firm.
Before serving, let the ice cream sit at room temperature for a few minutes to soften slightly for easier scooping.