Add the Guinness beer and cubed butter to a saucepan over medium heat, and once the butter has melted, stir in the cocoa powder and sugar. Beat the sour cream, eggs, and vanilla extract together and fold this mixture into the melted butter mixture in the saucepan. Stir in the flour and baking soda and pour the chocolate cake batter into a greased 10-inch springform cake pan. Press 3 empty Guinness beer cans into the chocolate cake batter in the springform pan.
For the chocolate Guinness sauce, divide the Guinness beer, cocoa powder, sugar, melted butter, and melted chocolate evenly between the 3 empty Guinness beer cans, pouring the ingredients directly into the cans. Transfer the cake pan to a preheated oven and cook at 325°F for 45-60 minutes. After baking, carefully remove the springform ring and base and let the cake cool for 2 hours.
After 2 hours, carefully remove the Guinness beer cans from the cake, swirl them around to combine the ingredients inside, and pour the chocolate Guinness sauce inside each can into one of the holes in the cake.
For the Baileys frosting, whip the cream cheese, gradually add in the powdered sugar, stir in the Baileys Irish cream, and fold in the whipped cream. Spread the frosting over the top of the chocolate Guinness cake.
For the chocolate ganache, fill a large glass milk bottle with the chocolate chips and heated heavy cream. Secure the bottle with a lid and shake the bottle until the heavy cream has melted the chocolate chips and the two ingredients have mixed together to create a ganache. Unscrew the lid and let the chocolate ganache cool to room temperature. Meanwhile, freeze a glass straw for 30 minutes.
Dip the frozen glass straw into the chocolate ganache in the glass bottle, gently swirl it around, slowly pull it out of the glass bottle, and wait for the chocolate ganache to set on the frozen straw. You can store the leftover chocolate ganache for later or use it to decorate the sides of the chocolate Guinness cake. Push the chocolate-filled straw into the center of the chocolate Guinness cake and carefully place an empty Guinness beer can upside-down on the angled end of the straw.