Season chuck roast generously with salt and pepper.
Heat olive oil in a large skillet over medium high heat.
Sear chuck roast on both sides until golden brown.
Transfer browned roast beef to a slow cooker.
Add chili powder, cumin, cayenne, diced onion, minced garlic, green chilis, chipotle peppers and beef broth to the slow cooker.
Cover and cook on low until beef shreds easily, about 8-9 hours.
Remove beef from the slow cooker and transfer it to a large bowl. Shred beef using two forks.
Strain juices in the slow cooker through a mesh strainer. Discard peppers.
Add a few tablespoons of the strained juices to the shredded beef to moisten.
Heat a table spoon butter in a large skillet over medium heat.
Place a flour tortilla in the pan.
Top with a layer of shredded Jack cheese to cover the tortilla.
Place about a ¼ cup of shredded beef onto one half of the tortilla.
Fold the tortilla in half.
Fry on both sides until cheese is melted, beef is heated through, and the tortillas are a crisp golden brown.
Serve immediately with a side of the juices for dipping.
Top with a dollop of sour cream if desired.