Cut tops off garlic heads to expose cloves. Place cloves on a sheet of foil. Drizzle liberally with olive oil and season with salt and pepper. Wrap up into a package and bake at 400 for 45-60 minutes, until cloves are very soft. Set aside to cool. When cool enough to handle squeeze soft garlic from papery skins into a small bowl. Mash well with a fork.
Cook bacon until just crisp and drain. Reserve drippings. Saute onion and shallot in drippings for 20 minutes until beginning to golden. Add garlic. Add sugar and salt and cook 3-5 more minutes. Sprinkle with flour and cook and stir to form a roux. Slowly pour in beer and mustard.
Put broth into slow cooker [lined or sprayed]. Add cooked onion mixture and Worcestershire sauce. Stir. Cover and cook on low for 6-7 hours
Garnish soup with Gruyere toast and crumbled bacon