Preheat oven to 350°F (175°C). Prepare two 9-inch cake pans.
In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, salt, and espresso powder.
Add milk, oil, eggs, and vanilla. Mix until smooth.
Slowly add boiling water and mix until fully combined. The batter will be thin.
Divide batter evenly between pans.
Bake for 30–35 minutes or until a toothpick comes out clean.
Cool for 10 minutes, then transfer to a wire rack to cool completely.
Frost with chocolate buttercream to complete this best chocolate cake recipe.