*Makes 12 enchiladas
1 medium onion, chopped fine
1 jalapeno, seeded and chopped fine
1 teaspoon canola oil
3 medium cloves garlic, minced
2 tablespoons chili powder
2 teaspoons ground cumin
3 teaspoons sugar
2 (8-oz) cans tomato sauce
1 cup water
1 1/2 pounds boneless, skinless chicken breasts (about 3 large chicken breasts)
1 cup shredded sharp cheddar cheese
1 cup shredded Monterey jack cheese
1/2 cup minced fresh cilantro
12 (6-inch) soft corn or flour tortillas (fajita-size for flour tortillas)
salt and ground black pepper
In a large saucepan, combine the onion, jalapeno, 1/2 teaspoon salt, and oil. Cover and cook over medium-low heat, stirring often, until the onions and peppers have softened, 8-10 minutes. Stir in the garlic, chili powder, cumin, and sugar, and cook until fragrant, less than 30 seconds. Stir in the tomato sauce and water. Bring to a simmer.
Nestle the chicken into the sauce. Reduce heat to low, cover, and cook until chicken is cooked through, about 12-20 minutes, depending on the size and thickness of the chicken breasts you are using. Transfer the chicken to a plate, and set aside to cool. Continue to simmer the sauce over medium heat until slightly thickened, about 5 minutes.
Strain the sauce through a strainer into a medium bowl, pressing the onion mixture to extract as much liquid as possible. Season sauce with additional salt and pepper to taste. Transfer the leftover onion mixture from the strainer to a large bowl and set aside.
Shred the chicken into bite-sized pieces. Add to the onion mixture in the large bowl. Also stir in 1/4 cup of the enchilada sauce, 1/2 cup cheddar cheese, 1/2 cup Monterey Jack cheese and the cilantro. Toss to combine.
Stack the tortillas on a plate and cover with plastic wrap; Microwave on high until warm and pliable, 40-60 seconds. Spread the tortillas on a clean work surface, and spoon 1/3 cup of the chicken mixture evenly down the center of each. Tightly roll each tortilla and lay seam-side down in a greased 9x13 inch baking dish.
Heat oven to 400 F. Pour the enchilada sauce evenly over the top of the enchiladas. Top with the remaining cheese. Cover dish with foil and bake 20 minutes, or until heated through.
Remove foil and bake another 5 minutes, until cheese browns. Remove from oven and let stand 10 minutes before serving.
Serve with sour cream, guacamole, salsa, additional cilantro, if desired.