In a medium sauce pan, whisk together the non-dairy milk, coconut milk, sugar, cocoa powder, and cornstarch while cold. Put over medium heat and continue to whisk. It will come together as it heats up. Bring to a simmer whisking often, and cook for about 3 minutes until the sugar has dissolved, and the mixture thickened into a fudge sauce. Remove from heat and whisk in the vanilla extract.
Pour the fudge sauce into the molds and freeze overnight.