Preheat oven to 350 degrees. Butter a 10-12 cup bundt pan and dust with flour or cocoa powder. I use the Baker's Joy spray that's grease AND flour.
In a large bowl, add in the cocoa powder and boiling water. Whisk until smooth. Set aside to cool.
After it's cooled, add in the vanilla and mayonnaise. Whisk until incorporated.
In a separate large bowl, whisk together flour, baking soda, sugar, and salt.
Add the chocolate mixture into the bowl of dry ingredients and beat with a hand mixer on medium for about 1 minute.
Pour the batter into the prepared bundt pan.
Place into the oven and bake for 30 - 45 minutes or until done. Insert a toothpick into the center of the cake and if it comes out clean or with moist crumbs, it's done. Batter means bake it longer.
Let the cake cool in the pan for 10 minutes and turn turn out onto a wire rack to cool completely.
Once the cake is cooled, transfer to a cake plate.
Glaze
In a small saucepan, add in the heavy cream, corn syrup, salt, and chocolate chips. Place over medium heat and stir constantly until the chocolate is completely melted and smooth.
Let the glaze cool 15 - 20 minutes until it has thickened. Drizzle on top of the cooled cake.