Make the cake: In a small saucepan, bring the water to a boil, turn off heat and whisk in the cocoa until smooth. Let cool to room temperature.
Place the rack in the center of the oven, and preheat to 350 degrees F.
Butter 2 (8 by 2-inch) round cake pans, line the bottoms with circles of parchment and butter the parchment. Dust them with flour, shaking off excess flour. Set aside.
In the bowl of a standing mixer with the paddle attachment, add the cold butter, sugar, eggs and vanilla. Beat on slow to combine and raise to medium-high speed for 8 to 10 minutes until the butter is almost completely incorporated into the mixture.
Meanwhile, in a medium bowl, sift the flour, baking soda, baking powder and salt.
With the mixer on low speed, alternately add the flour mixture and the cocoa liquid in 2 additions of each, stopping to scrape the bowl occasionally, mixing just until combined.
Evenly divide the batter between the 2 cake pans (I weigh them to get them even.) Bake for 45 to 55 minutes until the cake springs back when gently pressed and a toothpick in the center comes out clean. Cool in the pans 10 minutes, then place on wire racks to finish cooling completely.
Make the frosting: Put the chocolate chips in a heat proof bowl and place over a saucepan of simmering water, do not let the water touch the bottom of the bowl. Stir the chips occasionally until melted, and remove from the heat to cool.
In a medium mixing bowl, sift together the confectioners' sugar, cocoa and salt and set aside.
In the bowl of a standing mixer with the paddle attachment, beat the butter and the cream cheese until it is light and fluffy.
On low speed, slowly add the confectioners' sugar mixture to the butter mixture, combining well. Add the melted chocolate and the sour cream and vanilla, mixing just until combined. It's best to use it as soon as soon as it is made.
To assemble the cake: If the layers are a little uneven, then level the top of each layer. Using a serrated knife, split the first layer in half and place on a cake plate. Spread 1 cup of the frosting on top of the layer and spread to the edges. Add the next layer and spread another cup of frosting over it. Split the other layer in half, spread with another 1 cup of frosting, turn the top layer upside down so that the bottom is on top, and pile on the rest of the frosting, evenly spreading it all over the top and the sides, swirling as you go. Yum!
(Hints: I stick a 12-inch wooden skewer in the center of the cake to secure it while I frost it, and remove it before finishing frosting the cake. And, I lay strips of waxed paper under the cake to keep the cake plate clean as I frost the cake.).