Prepare: Thaw, peel and devein shrimp, then rinse and pat dry. Cook the sausage. Slice the garlic cloves. Crush the saffron threads. Scrub the mussels, then remove the beards and rinse.
Cook the paella: In the slow cooker, combine 2 cups broth, rice, tomatoes, sausage, garlic, bay leaf, and saffron. Cover and cook on LOW for 2 hours or until rice is nearly tender. Stir in peas, wine, and lemon juice. Top with shrimp (do not stir). Increase heat to HIGH. Cover and cook for 1 hour more or until shrimp turn opaque.
Cook the mussels and finish: In a large skillet bring the remaining 1/2 cup broth to a simmer over medium heat. Add mussels to skillet. Cover and simmer 3 to 6 minutes or until mussels open. Discard any unopened mussels. Add to paella. Serve in bowls with crusty bread.
notes
Adapted from "Better Homes & Gardens: Fast or Slow" (p. 123)