Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder, and salt.

In a separate bowl, whisk together eggs, milk, oil, and vanilla extract.

Add the wet ingredients to the dry ingredients and mix until just combined.

Carefully pour in the boiling water and whisk until the batter is smooth and thin.

Pour batter evenly into the prepared cake pans.

Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.

Let cakes cool in pans for 10 minutes before inverting onto wire racks to cool completely.

In a large bowl, cream together softened butter and cocoa powder until smooth.

Gradually add powdered sugar, alternating with milk, beating until smooth and creamy.

Stir in vanilla extract.

Place one cooled cake layer on a serving plate.

Spread about half of the frosting over the first layer.

Top with the second cake layer and frost the top and sides of the cake with the remaining frosting.