Slow cooker french onion soup - loads of flavor, caramelized onions, and CHEESE!
Add butter and onion rings to the largest pan/skillet you have and saute over medium-high heat for about 10 minutes or until onions are translucent and start to brown. Cover and cook about 5 minutes longer to let them caramelize a little more.
Transfer onions to slow cooker. Add garlic, broth, and bay leaf. Cover and cook on high 3-4 hours or on low 6-8 hours (or up to 10).
About 20-30 minutes before serving, preheat oven to 420 degrees. Place slices of bread in a single layer on a baking sheet. Place in preheated oven for about 5 minutes, then flip the bread slices over and return to oven for another 5 minutes or so until bread is dried and crunchy. Set aside.
Place oven-safe bowls on the baking sheet. Fill each with soup from the slow cooker. Place 2 slices of swiss cheese (overlapping) on top of the soup so the edges are hanging over the sides of the bowls. Bake about 10 minutes until cheese is melty. Serve with crusty bread and garnish with parsley if desired.