Cheesy Chicken and Broccoli Soup | America's Test Kitchen

Ingredients

• 3 tablespoons unsalted butter
• 1 onion, chopped fine
• 1¼ teaspoons table salt
• 1 teaspoon pepper
• 2 tablespoons all-purpose flour
• 3 cups chicken broth
• 2 (6- to 8-ounce) boneless, skinless chicken breasts , trimmed and halved lengthwise
• 1 pound broccoli florets , cut into ½-inch pieces
• 1 cup heavy cream
• 8 ounces sharp cheddar cheese , shredded (2 cups)
• 4 ounces American cheese , chopped (1 cup)