Steak Tostadas with Cilantro Sour Cream

Name: Steak Tostadas with Cilantro Sour Cream
Ingredients: 4 flour tortillas (6-inch); 1 cup shredded Manchego cheese (4 ounces); Reserved 2 cups mushrooms and steak, thinly sliced against the grain, from Seared Steak with Roasted Mushrooms and Spinach Salad; 1 package (10 ounces) frozen corn kernels, thawed and patted dry; 4 scallions, thinly sliced; Coarse salt and ground pepper; 1/2 cup reduced-fat sour cream; 1/4 cup chopped cilantro, plus more for garnish; 2 tablespoons fresh lime juice, plus lime wedges for garnish