Dark chocolate cake layers with a light and fluffy vanilla buttercream.
Preheat the oven to 350 degrees F. Prepare three 8-inch or four 6-inch round cake pans by spraying the bottom and sides with nonstick spray, lining the bottom with parchment paper, and spraying the parchment paper.
Add wet ingredients to the dry ingredients, and mix on low speed until combined. Batter will be thin. Scrape sides and mix for another 30 seconds. Divide batter evenly among prepared pans (I like to use a kitchen scale to ensure the batter is evenly distributed - about 15 to 16 ounces in each 8-inch or 12 ounces in each 6-inch).
In the bowl of a stand mixer fitted with a paddle attachment, cream the butter for about 2 minutes. This will soften the butter without it having to be warm.
With the mixer on low speed, gradually add the sifted powdered sugar, one cup at a time, mixing a little in between each addition.
With mixer on medium speed, add whipping cream, vanilla and salt.
Turn the mixer to medium-high speed and beat for an additional 5 to 7 minutes. The frosting will become lighter in color and texture.
Before spreading on your cake, spend a couple minutes mixing the buttercream by hand with a wooden spoon to push out the air pockets.