In small skillet over medium heat, add oil and sauté onions and jalapeño for 1 to 2 minutes. Stir in cumin and cayenne. Remove from heat. Add beans and bean broth to onion and pepper mixture in food processor. Pulse until not quite smooth. Add lime juice and salt. Taste and adjust flavors.
Jalapeños have been bred to be milder than they used to be. To find a hot one, you really must taste. If you want more heat, just leave in the seeds and membranes.