Frosting

1. In a heavy bottom saucepan brown the butter. Mix constantly, over low-medium heat, do not walk away. You will start to see it foam up then brown flecks will appear. (Check out this detailed post on how to brown butter)
2. When the brown flecks appear and you smell a nutty aroma the butter is done. Pour into a heatproof container to set up, place in the fridge, mix every 20 minutes or so as the butter cools and resolidifies to evenly distribute the brown butter flecks.

Cake

1. Preheat oven to 350F/180C and grease a 10 cup bundt pan and set aside.
2. In a saucepan over low-medium heat cook Guinness for 10 minutes, the liquid will reduce. Add in butter and mix until mostly all melted. Take the pot off the heat and mix in sugars and molasses, let cool for 5-10 minutes.
3. In a large bowl whisk together flour, baking soda, baking powder, ginger, cinnamon, nutmeg, and cloves.
4. In the cooled Guinness mixture whisk in eggs and vanilla. Make sure the eggs are fully combined into the batter. 
5. Pour wet mixture into the dry ingredients, and use a spatula to gently mix until just combined then fold in sour cream, be careful not to overmix. 
6. Bake for 35-45 minutes, until the cake bounces back when you gently press/ touch the center or a toothpick inserted comes out with only moist crumbs. Let cake cool on a wire rack for 10 minutes before inverting on to a rack. Frost when the cake when it is completely cool.

Frosting

1. Set browned butter on the counter to come to room temperature.
2. In the bowl of an electric mixer fitted with a paddle attachment or a large bowl with an electric mixer beat the browned butter for 1 minute, it should be light and fluffy.
3. Add in vanilla bean paste, salt, and powdered sugar, and cream mixing on low, once fully combined increase the speed and beat for five minutes to get a super fluffy, light buttercream.
4. Frost cake to your liking, I used a round open tip. Store in an airtight container on the counter or fridge for 4-5 days.