# The Ingredients You'll Need:
→ Pasta
01 - 12 oz egg noodles
→ Seafood
02 - 2 cans (6 oz each) tuna in water, drained
→ Vegetables
03 - 1 cup frozen peas, thawed
04 - 1 small onion, finely chopped
05 - 2 cloves garlic, minced
06 - 1 cup sliced button mushrooms, optional
→ Sauce
07 - 2 tablespoons unsalted butter
08 - 2 tablespoons all-purpose flour
09 - 2 cups whole milk
10 - ½ cup sour cream
11 - 1 teaspoon Dijon mustard
12 - ½ teaspoon salt
13 - ½ teaspoon black pepper
14 - ½ teaspoon dried thyme
→ Cheese
15 - 1 cup shredded cheddar cheese
→ Topping
16 - 1 cup crispy fried onions
# Step-by-Step Instructions:
01 - Preheat oven to 375°F. Lightly grease a 9 x 13 inch baking dish.
02 - Boil egg noodles according to package instructions until al dente. Drain and set aside.
03 - Melt butter in a large skillet over medium heat. Add chopped onion and mushrooms, sauté for 4 to 5 minutes until softened. Add garlic and cook for 1 minute.
04 - Sprinkle flour over the sautéed vegetables and stir for 1 minute. Gradually whisk in milk while stirring constantly. Cook for 3 to 4 minutes until the sauce thickens.
05 - Remove skillet from heat. Stir in sour cream, Dijon mustard, salt, black pepper, and dried thyme until well incorporated.
06 - Mix drained tuna, thawed peas, shredded cheddar, and cooked noodles into the sauce gently until evenly combined.
07 - Transfer mixture evenly into the prepared baking dish.
08 - Evenly sprinkle crispy fried onions over the casserole surface.
09 - Bake uncovered for 25 to 30 minutes, or until the casserole is bubbly and the topping is golden brown.
10 - Let the casserole stand for 5 minutes before serving to allow it to set.
