Preheat oven to 350 degrees F and line muffin tin with baking cups.
In the bowl of a stand mixer, mix flour, cocoa, sugars, baking powder, baking soda, and salt.
Add the buttermilk, eggs, vegetable oil, and vanilla. Mix until smooth. Scrape bowl as needed.
With the mixer on slow speed, add the hot water and mix until combined.
Use an ice cream scoop or 1/4 cup measuring cup to fill baking cups 2/3 full. Bake for 16-18 minutes or until toothpick comes out clean. Let cool in pan for 5 minutes and then move to a cooling rack to cool completely.