Place roast in a large saucepan with a tight-fitting lid. Cover roast with water and simmer on low for 30 minutes. Increase heat to medium/high and brown roast on all sides. Once the water has boiled away and the roast is browned, add beef broth, vinegar, chili powder and cumin. Cover tightly, reduce heat to low and simmer for 1 1/2 to 2 hours or until beef falls apart. Shred the beef. Place shredded beef back into saucepan with all the juices and cool to room temperature.
In a large skillet, saute onion util soft. Mix in flour and green chilies. Stir for 2 minutes to cook off the flour taste. Stir in sour cream and 2 cups of the Monterey Jack cheese. Cook on low for 10 minutes, stirring often, until the cheese is melted and mixed thoroughly. Set aside and let cool.
In a large heavy skillet, heat the olive oil. Fry the tortillas in the hot oil for 30 seconds on each side. Drain on paper towels.
Preheat oven to 375 degrees. Spread 4 tablespoons of sour cream mixture down the center of the tortilla. Top with the same amount of the beef mixture (yes, this will be juicy and messy). Roll up and place seam side down in baking dish. Repeat for each tortilla, until you are out of filling. Sprinkle with remaining Monterey Jack cheese.
Bake in pre-heated oven for 30 minutes or until cheese is melted and bubbling.
**Note: If you prefer a milder dish, omit the 4 ounce can of jalapeno peppers and replace it with another can of diced green chilies.
I serve each enchilada on a bed of shredded lettuce sprinkled with diced tomatoes. I top each enchilada with a dollup of sour cream and serve with a side of salsa.