Saute onion in olive oil over medium heat, stirring occasionally, until it begins to caramelize, about 15 minutes. Add garlic and cook 1 minute. Add sausage and cook 1-2 more minutes. Season with salt & pepper.
Place onion mixture in the bottom of greased slow cooker. Top with collards. Pour in beer and broth. Cover and cook on low 6-8 hours or high 3-4 hours, stirring halfway through cooking if possible.
Notes
*remove leaves from center stems and tear into smaller pieces