Step 1

Place chopped chocolate in a large heatproof bowl.

Step 2

In a medium saucepan, combine heavy cream, Baileys, and butter. Cook over med heat, stirring often until it just barely starts to simmer.

Step 3

Pour hot cream over chopped chocolate and cover bowl with plastic wrap. Let sit 5 minutes.

Step 4

Stir gently with a spatula until completely smooth. If needed, place over a double boiler and stir until all chocolate has melted.

Step 5

Place plastic wrap directly on top of chocolate ganache. Allow to thicken and set overnight.*

Step 6

Preheat oven to 350F, grease three 6" round baking pans and dust with cocoa powder. Line bottoms with parchment.

Step 7

Place flour, sugars, cocoas, baking powder, baking soda, and salt into the bowl of a stand mixer fitted with a paddle attachment. Stir to combine.

Step 8

Place Guinness into a small saucepan and heat until just simmering.

Step 9

In a medium bowl whisk buttermilk, eggs, oil, and vanilla. Temper this mixture with the heated Guinness -- pour hot Guinness into the bowl very slowly while whisking egg mixture quickly.

Step 10

Add wet ingredients to dry and mix on medium for 2-3 mins. Batter will be very thin.

Step 11

Pour evenly into prepared pans. I used a kitchen scale to ensure the batter is evenly distributed.

Step 12

Bake until a cake tester comes out mostly clean. A total of 30-35mins.

Step 13

Cool 10 minutes in the pans then turn out onto a wire rack to cool completely.

Step 14

Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.**

Step 15

Place bowl over a hot water bath on the stove and whisk constantly until the mixture is hot (160F) and no longer grainy to the touch (approx. 3mins).

Step 16

Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).

Step 17

Switch to paddle attachment. Slowly add cubed butter and mix until smooth.

Step 18

Add Baileys and vanilla and whip until smooth.***

Step 19

Cut each layer of cake in half horizontally.

Step 20

Place one layer of cake on a cake stand or serving dish. Top with about 1/2 cup buttercream, spread evenly. Repeat with remaining layers alternating buttercream with ganache. Frost and smooth the outside with a thin crumb coat. Chill for at least 20mins until firm and set.****

Step 21

Frost the chilled cake with the remaining ganache. It will start to set quicjkly against the cold cake.

Step 22

To smooth the top and sides of the cake, use a metal bench scraper and offset spatula that have been run under hot water (wipe them off before use). Keep heating the scraper/spatula and repeat the process until the sides and top are smooth.

Step 23

Using the remainder of the buttercream, do a rope border on the top using a Wilton 6B piping tip.

Step 24

Decorate bottom with chocolate flakes if desired.