Preheat the oven to 350 degrees.
Grease a 10-12 cup Bundt pan; set side.
In a stand mixer fitted with the blade attachment, add the cake mix and sugar to the mixer bowl. Alternatively, you can blend with an electric, hand-held mixer.
On the lowest speed setting, combine the dry ingredients for approximately 30 seconds.
Add the eggs, buttermilk, melted butter, vanilla, mayo, and butter flavoring, if using.
Combine together on low for about 30 seconds, or until most all the ingredients are moistened. Then turn to medium speed and blend for 2 minutes, scraping the blade and bowl, as needed.
Scrape all the batter into the greased Bundt pan and spread the batter evenly in the pan. Smooth the top.
Bake for approximately 40 to 45 minutes. Bake times are approximate; bake according to your oven’s heating. You can begin checking for doneness around 40 minutes if your oven runs hot. The cake is done when a few crumbs are attached to a toothpick inserted into the cake.
When the cake is done, pull it from the oven. Then, make the glaze, so the cake has about 5 to 8 minutes to slightly cool.
In a small saucepan over medium-low heat, combine all the glaze ingredients and stir until the butter is melted and the sugar is dissolved. Do not let the mixture boil. This should only take a matter of minutes.
Poke holes into the cake with a spoon handle, chopstick, or other utensil handle.
While the cake is still hot in the pan, drizzle about ¾ of the glaze over the cake as it will soak into the holes. Reserve the remaining ¼ of the glaze for after the cake has been inverted.
After pouring the glaze over the hot cake, allow the cake to soak up the glaze for 30 minutes.
Now, invert the cake onto a cake stand or cake plate/platter and allow it to cool.
Before serving, reheat the remaining glaze and brush or pour over the top of the cake, and serve.
Any leftovers can be kept in an airtight container for up to 4 days.