Preheat oven to 350º F. Grease 3-8 inch or 2-9 inch round cake pans and lightly dust with flour. I like to make 3, and use 2 for the layer cake and set the 3rd aside for kids that don't like the frosting and my sisters with nut allergies.
In mixing bowl (I use my Kitchen Aid), add flour, sugar, cocoa, baking powder, baking soda, and salt. Stir until well combined.
Add milk, vegetable oil, eggs, and vanilla to flour mixture and mix together on medium speed until well mixed. Reduce the speed to low and add boiling water to the cake batter a little bit at a time. Once the water is all mixed in, beat on high for about 1 minute.
Evenly distribute cake batter between the three 8x8 pans (or two 9x9) prepared cake pans.
Bake for 30-35 minutes, or until a toothpick or cake tester inserted in the center comes out clean.
Make frosting while cake is baking, as it needs an hour to cool.
Remove from the oven and allow to cool for about 10 minutes. Remove from the pan and cool completely.