Place a large pot of salted water over high heat and bring to a boil. Once boiling, add the egg noodles and cook according to the package instructions.
While you are waiting for the water to come to a boil, place a large skillet over medium heat and melt the butter. Once the butter has melted, sprinkle the flour in the pan and stir while letting the butter flour mixture cook for about 1 minute.
Whisk in the seafood or chicken stock and let the liquid cook until it has slightly thickened, about 5 minutes. Add the half and half and the mustard and bring the mixture back up to a bubble.