In a large skillet over medium heat, saute the onion, garlic, and jalapenos until softened and fragrant. Add the beef and cook completely.
Use a citrus reamer to add the juice of four limes to the mixture, and stir in the cumin. Add salt and pepper to taste, and stir in the cilantro.
To make the sauce, heat the vegetable oil in a saucepan over medium heat. Whisk in the corn starch until thickened, about 1 minute. Whisk in the chili powder, tomato sauce, salt, cumin, oregano, sugar, and cayenne pepper. Slowly pour in the chicken stock, whisking briskly while doing so.
To assemble, pour the sauce into a shallow dish. Dip the corn tortilla into sauce, coating it lightly. Fill with roughly 1/3 cup of the meat mixture and wrap, placing seam side down into a baking dish. Continue until you've used up all of your ingredients.
Sprinkle shredded cheese over the top of the enchiladas and bake in an oven at 350F for 20 minutes, or until the cheese has melted. Serve with cilantro or sour cream as a garnish.