Step 1

Dice 1 medium yellow onion (about 1 1/2 cups). Mince 2 garlic cloves. Grate 4 ounces sharp cheddar cheese on the large holes of a box grater (about 1 cup). Drain 2 (5-ounce) cans tuna, then flake the tuna into bite-sized pieces with a fork.

Step 2

Melt 2 tablespoons unsalted butter in a large heavy-bottomed pot or Dutch oven over medium heat. Add the onion, garlic, 1/2 teaspoon dried thyme, and 1/4 teaspoon of the kosher salt. Cook, stirring occasionally, until softened, 4 to 5 minutes.

Step 3

Sprinkle with 2 tablespoons all-purpose flour. Cook, stirring occasionally, for 1 minute to cook the floury taste out. Add 2 cups water and scrape up any browned bits from the bottom of the pot. Add 2 cups whole or 2% milk, 1 tablespoon Dijon mustard, and the remaining 1 1/4 teaspoons kosher salt. Stir to combine and bring to a boil over high heat.

Step 4

Add 8 ounces dried wide egg noodles. Reduce the heat to medium low and simmer, stirring often, until the noodles are tender, 8 to 9 minutes. Meanwhile, If using crackers, place 8 buttery crackers in a small plastic zip-top bag and crush with a rolling pin into coarse crumbs.

Step 5

Add the tuna, cheese, and 1 cup frozen peas. Stir until the peas are warmed through and the cheese is melted, about 1 minute. Turn off the heat. Add 1/3 cup sour cream and stir until combined. Taste and season with more kosher salt and black pepper as needed. Serve sprinkled with the cracker crumbs and chopped fresh parsley if using.