Preheat oven to 350°F (175°C). Grease and parchment-line two 9-inch round cake pans.
In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add the milk, vegetable oil, eggs, and vanilla. Beat on medium speed for 2 minutes.
Reduce speed to low. Carefully and slowly pour in the boiling water until just combined. The batter will be thin.
Divide evenly into pans and bake for 30-35 minutes until a skewer comes out clean.
Cool in pans for 10 minutes before turning out onto wire racks to cool completely.