Heat butter in a skillet over medium heat. Add onion, jalapeño, and chipotle pepper and cook for 8 minutes. Add garlic, chili powder, and cumin and cook for one more minute. Season with salt and pepper.
Transfer onion mixture to a slow cooker and stir in broth and sweetener. Add beef tips and cook on low for 6 to 8 hours, until the meat is easily pulled apart with a fork. Shred.
Heat Mission Organics White Corn Tortillas in a skillet until warm and serve tacos with desired fixings.