Mushroom Quesadillas

Name: Mushroom Quesadillas
Ingredients: 3 tablespoons butter, plus more as needed; 10 ounces white mushrooms, sliced; 1/2 to 1 teaspoon chili powder; 1/2 teaspoon kosher salt; 1/4 cup coarsely chopped fresh cilantro leaves; Four 10-inch flour tortillas; 8 ounces shredded Monterey jack cheese (about 2 1/2 cups); 2 ounces crumbled feta cheese (about 1/2 cup); Optional garnishes: Sour cream, cilantro sprigs, salsa