Preheat oven to 350 degrees F. Grease and flour 2 (9-inch) cake pans.
In a large bowl with an electric mixer on low speed, beat granulated sugar, flour, 3/4 cup cocoa powder, baking powder, baking soda, salt, and coffee granules. Add 1 cup milk, oil, eggs, and 1 1/2 teaspoons vanilla to flour mixture and beat on medium speed until well combined. Reduce speed and slowly add boiling water until combined. (The batter will appear very thin, but that’s the way it should look.) Pour the batter evenly between cake pans.
Bake 30 to 35 minutes or until a toothpick inserted in center comes out clean. Let cool 15 minutes in pans, then remove from pans to cool completely on a wire rack.
To make Chocolate Frosting, place 1 cup cocoa powder in a large bowl. With an electric mixer on medium-low speed, beat in butter and 2 teaspoons vanilla until creamy. Add powdered sugar and 1/2 cup milk by adding 1 cup of powdered sugar at a time, followed by a little milk. Beat until thoroughly combined. After all powdered sugar and milk have been added and combined, turn mixer to high and beat 1 minute or until smooth and creamy.
Place 1 cake layer on a serving plate and spread a layer of frosting on top. Place second cake layer over that and frost top and sides with remaining frosting. Using the back of a spoon, create swirls in frosting. Let sit 30 minutes before serving.