Green Chile Smothered Burritos

Name: Green Chile Smothered Burritos
Ingredients: 2 lbs. lean ground beef; 1/2 onion, thinly sliced; 2 lbs. small red potatoes, halved then sliced; 2 teaspoons salt, or to taste; 3 teaspoons New Mexico red chile powder; 1 teaspoon cumin; 2 cloves garlic, minced; 2 cups water; For the sauce; 3 tablespoons butter; 3 tablespoons flour; 1 clove garlic, minced; 1 1/2 cups chicken stock; 1 1/2 cups milk, at room temperature; 1 teaspoon salt; 1 cup roasted, peeled and chopped Hatch green chile; 1/2 teaspoon oregano; For the burritos; 6-8 burrito-sized flour tortillas; 1 cup shredded cheddar cheese; Sour cream, for garnish (optional)