(You can prepare the fudge ripple up to two weeks ahead of time. It needs to be thoroughly chilled before layering into the ice cream.)
In a medium heavy saucepan, whisk together the sugar, corn syrup and cocoa powder, over medium heat. Whisking constantly, heat until the mixture begins to bubble at the edges and then just comes to a low boil. Remove from the heat, then stir in the vanilla. Let cool, then transfer to an airtight container and chill in the refrigerator thoroughly before using.
For the white chocolate cherry ice cream:
(The candied cherries can also be prepared up to two weeks ahead of time. Ensure they are prepared and ready before churning the ice cream.)
Chop up the white chocolate and place in a large bowl with a mesh strainer set over top; set aside.
Prepare an ice bath by mixing a handful of ice cubes with cold water; set aside.
In a medium saucepan, heat the milk, sugar, and salt over medium-low heat until warm. In a separate medium bowl, beat the egg yolks together. Slowly pour the warm milk into the bowl with the egg yolks, whisking constantly, then transfer the mixture back into the saucepan.
Heat the mixture over medium heat, stirring constantly with a heat-proof spatula, until the mixture thickens slightly. Pour the now-custard through the strainer over the white chocolate bowl. Stir the strained custard and white chocolate together until the white chocolate is completely melted and smooth. Add the cream and stir to combine. Transfer the bowl to an ice bath and stir until cool.
Partially cover the bowl and chill the ice cream mixture in the refrigerator at least 8 hours, or overnight. Then, freeze according to your ice cream maker's manufacturer's directions.
Fold the candied cherries into the just-churned ice cream. Spoon some of the fudge ripple into the bottom of the ice cream storage container, layer a few scoops of ice cream, then top with more fudge ripple. Repeat these layers until the fudge ripple and ice cream are all in the container. Avoid stirring, to keep the fudge ripple layered.