Preheat oven to 350°F. Line the bottom of two 8" round cake pans with parchment paper. Place your Guiness and butter in a large saucepan, and bring to a simmer over medium heat. Remove from the stove and add cocoa powder and whisk until mixture is smooth. Cool slightly, about 10 minutes.
Whisk flour, sugar, baking soda, and salt together in a bowl. In the bowl of your electric mixer, beat eggs and sour cream to blend. Add Guiness-chocolate mixture to egg mixture and beat just to combine. Add your dry ingredients and beat briefly on low speed. Using rubber spatula, give your batter a final stir. Divide batter equally among prepared pans. Bake cakes until tester inserted into center of cakes comes out clean, about 55 minutes. Cool cakes completely.
For the Bailey's Irish Cream Icing
Bailey's Irish Cream Icing Ingredients
Beat cream cheese in the bowl of an electric mixer until smooth, about 3 minutes. Add your butter and continue to beat another 2 minutes. Scrape down the sides of your bowl. Add icing sugar at low speed, until incorporated. Add vanilla and Bailey's. Beat your icing for 2 minutes at high speed to remove any lumps.
For the Sponge Toffee
Sponge Toffee Ingredients
1 1/4 cups granulated sugar
1/3 cup clear corn syrup
1/3 cup water
1 1/2 tablespoons baking soda
Line a 9" x 13" metal pan entirely with parchment paper. Secure the paper with shortening.
In large pot, stir together sugar, corn syrup and water. Set over medium heat and bring to boil. Cook, without stirring until candy thermometer reaches 300°F, or when a drop of hot syrup dropped into cold water forms hardens, about 10-12 minutes.
Remove from heat. Wearing oven mitts, be very careful and whisk in baking soda. The toffee will bubble up and rise very high in the pot
Pour into prepared pan. Let cool in pan on rack without disturbing, about 2 hours. Break into nuggets with a meat tenderizer, mallet or a spoon - use to apply all over you cake!
Once you have all three components of this cake ready to go, we can begin to assemble this pile of delicious goodness. If you want a full step-by-step you can watch the video here. Start off by removing your cakes from their pans and levelling them with a ruler and a serrated knife. Get used to this - it's a big part of the How To Cake It world! Now cut each cake in half horizontally.
Fill these moist layers with your sinfully good Bailey's cream cheese frosting and give your cake a crumb coat. Place it in the fridge to chill. In the meantime, let's all take out our frustrations out on some sponge toffee! What did sponge toffee ever do to us, except be sweet? Honestly. Nevertheless, we need to bash this wonderfully fragrant sponge toffee into nuggets. It really is fragrant. They should make a perfume from the scent of sponge toffee. Lightbulb! Next business venture.
Remove the parchment paper from your sponge toffee and place it back into the pan. Now use your mallet to break it into pieces. They will not be uniform, but that's what we are looking for. We want our pieces to be small enough to eat, but not yet dust. Sift through your pieces and place all the ones that make the cut into a bowl. Don't even think about throwing out all that sponge toffee dust! Have you thought of the possibilities? Throw that dust onto ice cream, toss it into your popcorn, make a chocolate bark and sprinkle it on top, eat it with a spoon, dissolve it in your bathtub and bathe in it. Just, please, do not waste it.
These nuggets are perfect as they are, but if you wish, we can jazz them up a little. You will need some edible lustre dust of the gold variety. Simply sprinkle about two tablespoons all over your sponge toffee nuggets and toss. This is golden - literally!
Let's get back to our cake and give it a good icing. Once complete, use the palm of your hand to press the sponge toffee nuggets all the way up the sides of your cake, and mound a big pile on top. Give your cake a once over and fill in any gaps with more sponge toffee.
Now for one last detail. It is St. Patrick's day after all. We need some luck.
Roll out your green fondant and cut 12 hearts - 8 small hearts and 4 medium hearts. Overlap your hearts, four at a time, face down, in a north, south, east, west pattern and pinch the tips together. Now invert your hearts and, voila, you have a four leaf clover! I wonder what the Gaeilge word for voila is....... Place all three clovers on top of your cake.
Look at the amazing cake you made! Now you get to eat it. Lucky you.