Whisk together the egg yolks and 1/4 cup of granulated sugar until smooth. Heat the whole milk in a saucepan over medium heat until it reaches 165°F.

Gradually pour the hot milk into the egg mixture while whisking constantly. Return to saucepan and cook on low heat until it thickens.

Strain the custard through a fine-mesh sieve into a large bowl. Whisk in the heavy cream, vanilla extract, and salt.

Cover the bowl and refrigerate the ice cream base for at least 4 hours or overnight.

Chop the dark chocolate into small pieces and melt it gently in a saucepan. Pour into a zip-top bag for easy drizzling later.

Once chilled, pour the ice cream base into your ice cream maker and churn according to the manufacturer's instructions, about 25-30 minutes.

During the last few minutes of churning, drizzle the melted chocolate into the mixing ice cream to create chocolate ribbons.

Transfer the ice cream to an airtight container, smooth the top, seal tightly, and freeze for several hours until firm.