Preheat oven to 350°F. Grease a 10-cup Bundt cake pan and lightly sprinkle with the unsweetened cocoa powder. Set aside.
2 teaspoons unsweetened cocoa powder
In a medium saucepan, heat the water until warm.
1 cup water
Add the butter, oil, and chopped semisweet chocolate. Cook on low, stirring constantly, until the chocolate is melted and the mixture is smooth, about 3-4 minutes.
¾ cup unsalted butter, ¾ cup canola oil, 4 ounces semisweet baking chocolate
Turn off the heat and stir in the sugar until smooth. Let cool for 5-10 minutes.
1½ cups granulated sugar
In a medium bowl, stir together the flour, cocoa mix, baking soda, and salt. Set aside.
3 cups All Purpose Flour, ¾ cup dry hot cocoa mix, 2½ teaspoons Baking Soda, ½ teaspoon kosher salt
Pour the cooled chocolate mixture into the bowl of a stand mixer fitted with the paddle attachment. Beat in the eggs one at a time until just combined.
3 large eggs
Slowly add the flour mixture and mix until just combined.
Add the buttermilk and vanilla extract and mix until just combined.
¾ cup buttermilk, 1 tablespoon pure vanilla extract
Fold in the chocolate chips and mini marshmallows.
1 cup milk chocolate chips, 1 cup mini marshmallows
Pour the batter into the prepared Bundt cake pan.
Bake the cake for 45 minutes, or until a toothpick comes out clean. Allow to cool for 10-15 minutes, then flip it onto a cooling rack. Cool completely before topping with the ganache.
After the cake cools, make the ganache. Place the heavy cream, butter, and chocolate in a microwave-safe bowl. Microwave these ingredients for 30 seconds at a time, stirring after each time until the mixture is melted, until smooth. Let cool for about 5 minutes, or until slightly thickened. Set aside.
⅓ cup heavy cream, 2 tablespoons unsalted butter, 4 ounces semisweet baking chocolate
Add the marshmallow creme to a large Ziplock bag and cut off one corner. Squeeze the bag to drizzle the creme on the cooled cake.
1 cup marshmallow creme
Drizzle the chocolate ganache onto the cake.
Sprinkle the cake with the marshmallow bits, if desired. Allow the ganache to fully set before slicing and serving.
Mini Marshmallow Bits