Preheat your oven to 375 degrees. Spray your bundt pan and then lightly dust with cocoa powder (this will help release the bundt cakes easier and the cocoa powder will not leave any white marks like flour does). Set aside.
Using a small saucepan over medium high heat, heat the chocolate milk and butter just until butter is melted. Remove from the heat and after a minute or so, add in the cocoa powder, stirring with a wire whisk. Once everything is combined, add the sugar and whisk until it has dissolved. Transfer the mixture to the bowl of your stand mixer and let cool for a couple minutes.
In a separate mixing bowl, combine the flour, baking soda, cinnamon and salt. To the wet ingredients, beat in the egg and vanilla extract. Slowly add in the flour mixture and continue to mix until incorporated.
Pour the cake batter into the mini wells of the bundt pan and bake for about 20-25 minutes or until a toothpick inserted comes out clean.
Remove the bundt pan from the oven and let cool for at least 15-20 minutes. Once cooled, gently run a butter knife or fork around the sides of each cake to gently loosen from the pan. Using a wire rack or large plate that will cover the entire bundt pan, place the wire rack on top of the mini bundt pan and flip to release the mini bundt cakes. Alternatively, you can remove each mini bundt cake gently with a fork.
To decorate: Using a pastry bag (or ziploc bag) with a ribbon decorating tip, fill the bag with the vanilla frosting. Starting from the top and working your way down, pipe a line across the front of each mini bundt cake, making sure to slightly overlap your lines so that you get the mummy effect. Place the eyes on and serve!