Preheat oven to 450 degrees F.
Slice potatoes and brussels sprouts lengthwise. In large bowl, quickly soak vegetables in beer. Place on rimmed baking sheet and top with onion, garlic, rosemary, and drizzle of olive oil. Bake 45 minutes, and stir midway through. Sprinkle roasted vegetables with kosher salt, break up the bacon, and add extra olive oil if desired.