Make the Ice Cream Custard: In a medium bowl, whisk the egg yolks to break them up. Add ¼ cup of the sugar and whisk to combine; set aside.
In a medium saucepan, stir together the cream, milk, remaining sugar and salt and place over medium-high heat. When the mixture approaches a bare simmer, reduce the heat to medium.
Ladle out a scoop of the hot cream mixture and, whisking the eggs constantly, add the cream to the bowl with the egg yolks. Repeat, adding another ladle-ful of the cream mixture to the bowl with the egg yolks, continuing to whisk. Pour the egg yolk mixture back into the saucepan.
Using a rubber spatula, stir the mixture constantly over medium heat until it is thickened and coats the back of the spatula (it should register between 170 and 175 degrees F on an instant-read thermometer), about 1 to 2 minutes.
Strain the custard through a fine-mesh sieve into a clean bowl and whisk in the vanilla extract. Place the bowl in an ice bath and stir the mixture occasionally until cool. Remove the container from the ice bath, cover and refrigerate until completely chilled, at least 2 hours or overnight.
Make the Fudge Ripple: In a small saucepan, whisk together the sugar, water, cocoa, corn syrup and salt. Place the pan over medium-high heat and whisk until the mixture comes to a full simmer. Once the mixture has simmered and the sugar is completely dissolved, remove from heat and add the chopped chocolate. Let sit for 1 minute, then whisk until melted and smooth. Whisk in the vanilla extract. Allow to cool to room temperature, then place in an airtight container in the refrigerator and chill completely before using. (Any leftovers can be kept in an airtight container in the refrigerator for up to 2 weeks.)
Churn the Ice Cream: Freeze the ice cream according to the ice cream maker's instructions, adding the chopped almonds during the last minute of churning. As you transfer the ice cream to the storage container, alternate layers of the ice cream with drizzles of the fudge ripple. Once all of the ice cream is in the container, use a butter knife to gently swirl the mixture.
If you cannot find (or don't want to use) corn syrup in the fudge ripple, I would recommend substituting Lyle's Golden Syrup.