Beef and Broccoli Burritos with Monterey Jack Sauce

1/2 pound boneless chuck, cut into 1/4-inch cubes
1 tablespoon vegetable oil
1 1/4 cups finely chopped broccoli
1 small clove garlic, minced
1 small onion, minced
1/2 cup tomato purée
1/2 teaspoon chili powder
1/4 teaspoon ground cumin

Sauce:
3 ounces Monterey Jack cheese
1/2 cup sour cream
one 4-ounce can chopped green chiles
2 teaspoons fresh lemon juice
four 8-inch flour tortillas

In a large heavy skillet cook the chuck in oil over moderately high heat, stirring until it is just browned. Add broccoli, garlic, onion, tomato purée, chili powder, cumin, salt to taste, and 1/2 cup water. Cook mixture, covered, over moderate heat 15 to 17 minutes or until filling is thickened. Keep the filling warm, covered, over low heat. In a small saucepan, combine Monterey Jack cheese, sour cream, chiles, and lemon juice. Heat over moderately low heat until cheese is melted and keep warm, covered. Do not let sauce boil. Heat a dry 8-inch skillet and heat each tortilla, turning frequently, for 30 seconds or until soft. Transfer to a work surface. Spoon 1/4 of filling onto tortilla and roll up burrito. Arrange filled burritos seam side down on platter and nap with sauce. Serves 2.