Preheat and Prepare Pan:
Preheat your oven to 350°F (175°C). Grease and flour a bundt cake pan thoroughly to ensure easy release.

Mix Cake and Brownie Bases:
In a large mixing bowl, combine the chocolate cake mix and fudge brownie mix evenly.

Add Wet Ingredients:
Add the eggs, water, vegetable oil, and mayonnaise to the dry mixes. Beat on medium speed for about 2-3 minutes until the batter is smooth and well blended. The mayonnaise adds moisture and richness, making the cake tender.

Fold in Chocolate Chips:
Gently fold in the chocolate chips using a spatula, ensuring they are evenly distributed but not overmixed.

Pour Batter into Pan:
Pour the batter into the prepared bundt pan and smooth the top with a spatula.

Bake:
Bake for 50-60 minutes or until a toothpick inserted into the center comes out with a few moist crumbs (not wet batter). Oven times may vary, so start checking at 50 minutes.

Cool:
Allow the cake to cool in the pan for 15-20 minutes before inverting it onto a wire rack to cool completely.

Prepare Ganache:
While the cake cools, heat the heavy cream in a small saucepan over medium heat until it just begins to simmer. Pour the hot cream over the chocolate chips in a heatproof bowl. Let sit for 5 minutes, then stir until smooth and glossy.

Glaze the Cake:
Drizzle the ganache evenly over the cooled cake, allowing it to drip down the sides.

Serve and Enjoy:
Slice the bundt cake and serve. The combination of fudgy brownie texture with the lighter chocolate cake and silky ganache makes for an irresistible treat.