Heat olive oil in large skillet over medium-high heat. Add onions and both bell peppers and sauté until beginning to brown, about eight minutes. Add garlic and 4 teaspoons of cumin; stir one minute. Transfer mixture to 6-quart slow cooker. Add beans and chipotles, then 7 cups hot water. Cover and cook on high until beans are very tender, about 3 to 4 hours
Transfer two cups bean mixture to blender; puree until smooth. Return puree to remaining soup in slow cooker. Stir in lime juice, salt, and pepper. Adjust seasonings to taste; we found we needed more salt. Ladle soup into bowls
To make the cumin crema stir the ground cumin into the crème fraîche and season with salt and pepper, to taste
Spoon dollop of cumin crema over each bowl and serve