For the Chocolate Syrup
Whisk together 1/2 cup of the sugar, corn syrup, the hot water, and the cocoa powder in a small saucepan. Stirring occasionally, bring the mixture just to a simmer.

Remove the pan from the heat, whisk in 1/2 teaspoon of vanilla, and set aside to cool.

For the Cake Batter
Making sure the rack is in the lower third of the oven, preheat the oven to 350 F. Butter and lightly flour a 12-cup bundt pan and set aside.

In a medium mixing bowl, whisk together the salt, flour, and baking powder.

In the bowl of a stand mixer (or using a hand mixer) cream the butter and sugar until pale and fluffy (approximately two minutes). Scrape down the bottom and sides of the bowl and beat in the remaining 2 teaspoons of vanilla.

With the mixer speed reduced to low, beat in a third of the flour mixture just until the flour begins to disappear into the batter. Add the milk and the rest of the flour mixture, alternating additions. Beat just until the batter is smooth, making sure not to over-process the batter. Gently fold the chocolate chips into the batter.

In a mixing bowl, divide out a third of the batter and whisk with the chocolate syrup. Set the chocolate batter aside. Pour a third of the vanilla-chocolate chip batter into the prepared bundt pan and smooth the top with a spatula.

Top the layer with the chocolate syrup batter, smoothing again with a spatula. Repeat the process with the remaining third of the batter. Using a knife or wooden skewer, lightly swirl the batters using a continuous figure 8 motion until there is a marble effect.

Bake approximately 60-70 minutes, or until a toothpick inserted into the cake comes out clean and the cake springs back when lightly touched. Cool the cake completely on a wire rack. it is important that the cake is completely cool or there may be cosmetic damage when it is inverted. Invert the cake onto a serving platter and serve.