Bring a large pot of salted water to a boil. Cook the egg noodles al dente, according to package instructions. Drain well and set aside.
In a deep nonstick skillet, warm 2 tablespoons of the butter over medium-high heat. Once bubbly, add in the kielbasa and sauté for about 3 minutes until browned and crisp; transfer to a plate with a slotted spoon and set aside.
In the same pan with the rendered kielbasa fat, add onions, garlic, cabbage, and 2 more tablespoons butter. Reduce heat to medium and sauté, stirring frequently, until cabbage is tender, about 8 minutes (depending on how tender you like the vegetable.)
Add the cooked noodles and kielbasa to the cabbage mixture tossing to combine and heat through. Stir in the remaining 2 tablespoons butter, the mustard (f using), and season with the salt and pepper.
Serve immediately and enjoy!
