Combine water and sugar in a small saucepan and bring to a boil.
¾ cup water, 1½ cups granulated sugar
Reduce heat to low and sift in the cocoa powder.
¾ cup Dutch-processed cocoa powder
Then whisk in the vanilla, salt, and corn syrup.
1 tablespoon vanilla extract, ⅛ teaspoon sea salt, 1 tablespoon light corn syrup
Continue to cook for about 10 minutes, whisking often, until it starts to thicken.
Remove from heat and strain through a fine mesh sieve to remove any clumps.
Let cool completely, about 1 to 2 hours, before using.