Preheat oven to 350°F (175°C). Grease and flour two 8-inch round baking pans.

In a microwave-safe container, combine water and coffee granules and bring to boiling. Set aside.

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

Add eggs, milk, oil, and vanilla to the dry ingredients and beat on medium speed for 2 minutes.

Stir in the boiling coffee; the batter will be thin.

Pour batter evenly into the prepared pans and bake for 30 to 35 minutes or until a toothpick comes out clean.

Let the cakes cool in the pans for 10 minutes and then transfer to a wire rack to cool completely.

For the frosting, melt butter and mix with cocoa powder and salt.

Alternately add powdered sugar and milk until smooth.

Stir in vanilla and adjust consistency as needed.

Frost the cooled cakes with chocolate frosting.