In a medium saucepan, bring the guiness and butter to a light boil over medium heat.
Add the cocoa powder and whisk until smooth.
Remove from heat and set aside.
In a large bowl, whisk together the flour, sugar, baking soda and salt.
In the bowl of an electric mixer, beat together the eggs, sour cream and vanilla.
Add in the butter/Guinness mixture and mix until just incorporated.
Add the flour mixture and mix until just barely incorporated.
Pour into the bundt pan.
Bake for 55-60 minutes, or until a toothpick comes out with only a few crumbs on it.
Allow to cool in the pan for 10 minutes.
Turn the cake out onto a wire rack and cool completely.
Cover in plastic wrap anyplace the fridge overnight.
Salted Caramel Glaze:
In medium saucepan, bring the butter, brown sugar, heavy cream and salt to a rolling boil – stir constantly.
Boil for ONE minute, stirring constantly.
Remove the pan from the heat and stir in the vanilla.
Add about 1/2 cup powdered sugar and whisk until smooth.
Continue whisking in the powdered sugar a little at a time until you get the consistency that you want - you want it thick enough to pour nicely but not so thick that it won't drizzle.
Remove the cake from the fridge.
Place on a cake plate, and pour the salted caramel over the top.