Pre-heat oven to 400° and line baking sheet with foil and place baking rack on top in oven.
Add bacon to baking sheet and bake for 10 minutes.
Meanwhile in a small bowl, whisk together the sugar and Guinness until it's frothy.
Remove baking sheet from oven and with a silicone brush, brush one side of the bacon generously with beer and brown sugar.
Return to oven and bake another 10 minutes and then remove from oven again, flip bacon, and generously brush other side of bacon with beer and sugar mixture. Return to oven and let bake for another 10 minutes.
Remove from oven, and gently remove bacon from pan to a plate and let cool it cool completely, at least 30 minutes.