Six layers of rich, decadent chocolate and guinness, enrobed in a generous layer of dark chocolate ganache, sandwich clouds of peanut butter swiss meringue buttercream.
Prepare three (3) 6” round pans using your preferred method. I use a pastry brush to apply Wilton Cake Release.
Cut butter into cubes. In a heavy large saucepan over medium heat, bring the Guinness and butter to simmer .
When butter is melted, whisk in the cocoa powder until mixture is smooth. Remove from heat and let cool slightly.
Sift flour and baking soda into a large bowl, or onto a sheet of parchment paper. Add sugar and salt and whisk together.
Using the paddle attachment of your electric mixer, beat eggs and sour cream until blended. Add the Guinness mixture to the egg mixture and beat briefly, just to combine. Add flour mixture and beat briefly on slow speed.
Remove bowl from stand mixer. Using a silicone spatula, fold batter until completely combined.
Divide batter equally among prepared pans. Each of my 6” pans, when weighed, held 570 grams of batter.
Bake cakes until tester inserted into center of cakes comes out clean - that was 25 minutes in my oven. Baking time may vary depending on your oven.
Transfer cakes to rack; cool 10 minutes. Turn cakes out onto rack and cool completely.
To make the buttercream:
Using a clean towel and some lemon juice or vinegar, clean your mixing bowl, whisk attachment and utensils to remove any traces of grease.
Fill a heavy duty pot about a quarter of the way with water and place on the stove over medium heat to simmer.
Add egg whites, sugar and a pinch of salt to the bowl of a stand mixer and place over the pot of simmering water, ensuring the bottom of the bowl is not in contact with the water in the pot.
Whisk the sugar, egg white, salt mixture constantly, but gently, until temperature reaches 160°F.
Once at the correct temperature, remove from heat and dry the underside of the bowl with a towel before placing it on the stand mixer.
With the whisk attachment, begin to whip the meringue until it is thick, glossy, and the bottom of the bowl is no longer warm to the touch. Do not begin adding butter while the bowl is still warm.
Switch from your whisk to paddle attachment and with mixer on low speed, add butter cubes, one at a time, until incorporated. Continue to mix until it reaches a silky smooth texture.
Add vanilla and peanut butter, continuing to beat on low speed until well combined and silky smooth.