Ingredients
For the cake:
1 3/4 cups (220 g) all-purpose flour
2 cups (400 g) granulated sugar
3/4 cup (90 g) Cacao Barry Cocoa Powder - Extra Dark
2 teaspoons (10 g) baking soda
1 teaspoon (5 g) baking powder
1 teaspoon (9 g) salt
2 eggs, at room temperature, lightly beaten
1 cup (237 mL) strong, hot black coffee or espresso
1 cup (237 mL) buttermilk, room temperature
1/2 cup (119 mL) vegetable oil
1 tablespoon (15 mL) pure vanilla extract
For the Swiss Meringue Buttercream
5 large egg whites (150g)
1-1/4 cups (250 g) granulated sugar
1 pound (4 sticks) unsalted butter, softened, cut into cubes
2 teaspoons (10 mL) pure vanilla extract
pinch of salt
Instructions
For the cake layers:
Preheat oven to 350 F. Prepare 2 x 9" (or 3 x 8" for slightly shorter layers) cake pans with butter and flour or parchment paper.
In bowl of electric mixer fitted with the paddle attachment, sift all dry ingredients. Add remaining ingredients to mixture and mix for 2 minutes on medium speed (you may need the plastic splashguard that comes with mixer).
Divide among prepared pans. Batter will be liquidy.
Bake for 20 minutes and rotate pans in oven. Cakes are done when toothpick or skewer comes clean, about 35 minutes. Try not to overbake.
Cool on wire racks for 20 minutes then gently invert onto racks until completely cool.
For the Swiss Meringue Buttercream:
Wipe the bowl of an electric mixer with paper towel and vinegar, to remove any trace of grease. Add egg whites and sugar, and simmer over a pot of water (not boiling), whisking constantly, until temperature reaches 140°F, or if you don't have a candy thermometer, until the sugar has completely dissolved and the egg whites are hot.
With whisk attachment of mixer, begin to whip until the mixture is thick, glossy, and cool. Switch over to paddle attachment and, while mixing on medium speed, gradually add softened butter in chunks until incorporated, and mix until it has reached a silky smooth texture (if curdles, keep mixing and it will come back to smooth).
Add vanilla and salt and mix well.
Keep in airtight container in refrigerator for up to one week, leaving out at room temperature when needed, rewhipping in mixer for 5 minutes.
Can freeze for up to 6-8 weeks.
Source: http://sweetapolita.com/2010/11/rich-ruffled-chocolate-celebration-cake/