One 28-ounce can whole tomatoes, drained and 1/2 cup liquid reserved
2 chipotles in adobo
1 1/2 tablespoons vegetable oil
1 large white onion, thinly sliced
3 garlic cloves, very finely chopped
1 1/2 cups chicken stock or low-sodium broth
Salt
8 ounces tortilla chips
1 1/2 cups shredded chicken
1/4 cup freshly grated Parmesan cheese or queso añejo (see Note)
1/3 cup sour cream
1/4 cup finely chopped cilantro leaves