Add frozen egg noodles to a large pot of salted water that's come to a rolling boil.
Once the noodles float to the top and the water has re-reached a boil around the perimeter, set an 9 minute timer.
While the noodles boil, dice your onions and shred your rotisserie chicken.
Drain and rinse the egg noodles in cold water. Set aside.
In the same pot the egg noodles cooked in, melt a stick of salted butter.
Add the diced onions, stir, season with 1/2 teaspoon of kosher salt and cook over medium heat for 15 minutes.
Add the flour, stir and cook the raw flour taste out for 2 minutes. Stirring often.
To the flour add the chicken stock, Better than Bouillon, salt and pepper. Whisk and turn the heat to high. Once the consistency has thickened a bit, turn the heat back down to medium. Be sure to whisk this whole time to avoid the bottom burning.
Add the frozen vegetables (you want them frozen) to the pot along with the shredded chicken and cooked egg noodles. Stir with a wooden spoon, cover and allow the flavor to come together over low heat for 15-20 minutes. Stir occassionally. Taste and make sure the noodles are done to your liking. If they don't taste done, continue cooking.
The dish will continue to thicken the longer it sits. Serve with biscuits or ladle over mashed potatoes.