For the Cake:

1. Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
2. In a large bowl, sift together flour, sugar, cocoa powder, baking powder, baking soda, and salt.
3. In another bowl, whisk eggs, milk, melted butter, and vanilla extract until smooth.
4. Gradually stir the wet mixture into the dry ingredients until fully combined.
5. Slowly pour in the boiling water, stirring gently. The batter will be thin.
6. Divide evenly between pans and bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean.
7. Let cakes cool in pans for 10 minutes, then transfer to a wire rack to cool completely.

For the Buttercream Frosting:

1. Beat the butter until creamy.
2. Add powdered sugar one cup at a time, beating well.
3. Mix in milk, vanilla, and salt, and beat until fluffy. Adjust consistency with a little extra milk, if needed.
4. Frost the cooled cake layers and decorate as desired.