Stovetop Green Bean Casserole

Name: Stovetop Green Bean Casserole
Ingredients: 2 tablespoons kosher salt; 1 pound string beans, ends trimmed, beans cut in half; Ice cubes; 1 tablespoon unsalted butter; 12 ounces white mushrooms, washed, sandy ends (if any) removed, and sliced into 1/2-inch slices; 1 teaspoon cayenne pepper; 1 teaspoon Dijon mustard; 2 cloves garlic, peeled and minced (or put through a garlic press); 3 tablespoons all-purpose flour; 1 cup chicken stock; 3/4 cup heavy cream; 1 cup sour cream; 4 cups canola oil; 1/4 cup all-purpose flour; 2 teaspoons cayenne pepper; 3 medium shallots, peeled and cut into thin rounds; Kosher salt