Ultimate Cottage Pie

Name: Ultimate Cottage Pie
Prep time: 35 min
Cook time: 1 h
Total time: 1 h 35 min
Cuisine: British
Ingredients: ½ teaspoon baking soda optional; 1 tablespoon water; 2 pound Ground beef; ½ teaspoon salt; 2 tablespoons oil; 1 large onion chopped; 3 celery stalks diced; 2 carrots chopped small; ¼ cup all-purpose flour; 2 cups beef stock; 1 tablespoon soy sauce; A good handful of fresh parsley chopped; 8 ounces cremini mushrooms sliced; salt and pepper to taste; 1 tablespoon flour; ⅔ cup heavy cream; 2 garlic cloves thinly sliced; ¼ teaspoon freshly grated nutmeg; Salt and freshly ground black pepper to taste; 2 pounds russet potatoes peeled and cut into 1/8-inch-thick slices; 4 ounces cheddar cheese grated; ½ cup grated Parmesan