Preheat oven to 350F and grease a 9x13" baking pan with non-stick baking spray or butter.
In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder and salt. Set aside.
In a medium bowl, whisk together the milk, vegetable oil, vanilla and eggs.
Add the wet ingredients to the dry ingredients and mix until combined with a rubber spatula.
Add in the hot water and whisk until smooth.
Pour into the prepared baking pan and bake for 30-32 minutes or until a toothpick inserted into the center comes out with a few moist crumbs.
Let cool completely before frosting.
Buttercream Frosting Preparation
Using a handheld or stand mixer, beat the butter for 1 minute until creamy. Mix in 1 cup of powder sugar and with 1 Tbsp of milk/cream at a time, mixing well in between.
Mix in the cocoa powder and vanilla until smooth. Add more milk/cream if necessary for a spreadable consistency.
Notes
This cake tastes even better on the second or third day, and also great slightly chilled from the fridge. Perfect for any occasion!