To prepare the cake, preheat the oven to 350°F/180°C. Grease the bottom and sides of two 9-in. round cake pans with butter. Line pan bottoms with parchment paper.
In a mixing bowl, sift together the flour, cocoa, baking soda and salt.
In the bowl of an electric mixer fitted with a flat paddle, combine the oil, sugar, eggs and vanilla and beat on medium speed for 1 minute.
Reduce the speed to low and incorporate the cocoa mixture and the buttermilk in three additions. Start and end with the cocoa mixture, mixing thoroughly after each addition and scraping the inside surface of the bowl several times. Mix an additional 10 seconds after the last addition.
Spoon one half of the batter into each prepared pan. Place each pan on a baking sheet and bake for 30 - 35 minutes or until a toothpick inserted in the center comes out clean.
Cool on wire racks for 15 minutes. Invert cakes onto racks and remove the paper; cool completely.
To prepare the frosting, combine all ingredients, except vanilla and coloring, in a tempered glass or stainless steel bowl or in a double boiler.
Beat mixture on medium speed with a hand-held electric mixer for 1 minute.
Place bowl/pan over simmering water (the bottom of the bowl/pan should not touch the water) and continue to beat mixture on high for 7 - 8 minutes or until thick and shiny.
Remove from heat and add vanilla; beat for 1 - 2 additional minutes until the frosting holds medium firm peaks.
Add food coloring and beat until distributed.
To assembling the cake, place one layer on a serving tray and spread the top with a generous portion of icing, gently pushing it to the edge of the layer.
Place the second layer on top of the frosted layer; frost the top and sides of the cake with the remaining frosting.
Decorate the cake with candy, sprinkles, nuts, or grated chocolate.
Cake is best served the day it is assembled. Store covered at room temperature.
Recipe is included with our Kitchen Essentials from Calphalon 9" Round Cake Pan.