Silky Tortilla Soup

Name: Silky Tortilla Soup
Ingredients: 2 tablespoons extra-virgin olive oil; 1 large white onion, thinly sliced; 5 garlic cloves, thinly sliced; Kosher salt; 1 1/2 pounds plum tomatoes, halved; 4 chipotle chiles in adobo sauce, seeded and coarsely chopped; 8 cups chicken stock; Canola oil, for frying; 6 corn tortillas, halved and thinly sliced; 1 stick unsalted butter, diced; 4 cups shredded chicken, from one 2 1/4-pound rotisserie chicken; Crumbled queso fresco, dried chile and cilantro leaves, for garnish