Preheat oven to 350 degrees. Line a 12 cup muffin tin with liners and set aside. In a liquid measuring cup, combine the Cheerios™ and milk, stir gently and set aside.
In the bowl of a stand mixer, beat together the butter and sugar on medium speed until light, fluffy, and creamy, around 5 minutes. Beat in the eggs, one at a time, until thoroughly combined, then add the vanilla.
In a separate bowl, whisk together the flour, cocoa powder, cinnamon, and salt. Using a fork or small, slotted spoon, carefully remove the cereal from the milk and discard (or eat!).
With the mixer on medium-slow, gradually add 1/2 of the dry ingredients, then 1/2 of the milk, alternating until all ingredients are incorporated and a thick batter forms.
Using an ice cream scoop, divide the batter between the 12 muffin cups, filling them about 2/3 full each. Place in oven and bake for 15-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. All cupcakes to sit in the pan for 5 minutes before removing and allowing to cool completely on a wire rack.