Preheat the oven to 350 F. Line a muffin tin with 6 cupcake liners, or spray with cooking spray.
In a large bowl, sift or stir together flour, sugars, cocoa powder, baking soda, baking powder, and salt. Set aside.
In a mixing bowl, beat oil, egg, buttermilk, and vanilla together until completely mixed. About 1 minute. Slowly add dry ingredients into wet ingredients while mixing. Pour in hot water and mix together another minute. It's ok if the batter seems extra liquidy.
Pour batter evenly into muffin cups. Bake for about 18-22 minutes. When toothpick placed in the center of the cupcakes comes out clean, you know it is done.
Let the cupcakes completely cool before taking out of the pans and frosting.
To make the chocolate buttercream:
In a large mixing bowl, cream together butter and cocoa powder until it comes together. Add in powdered sugar, vanilla, salt and cream. Beat until light and fluffy. You may end up needing to add more powdered sugar or cream to get your desired consistency. Frost cupcakes.
Cupcakes will have the best results if made with room temperature ingredients. I like to pull my egg, buttermilk, and butter out of the fridge an hour or two before I start baking.You may need to add more or less powdered sugar and milk to get the desired consistency for the buttercream.I have given both cups and grams as measurements. Grams will be more precise, especially when measuring flour. If you don’t have a kitchen scale, no problem! Just lightly spoon flour into your measuring cup to insure its not packed in there. Light and fluffy is the key.