Boil the egg noodles in heavily salted water according to package directions until al dente. Drain, reserving a splash of pasta water, and set aside.

In a large skillet or Dutch oven, melt half of the butter over medium heat. Add the sliced onions and cook until softened and golden brown, about 5 to 7 minutes.

Add the remaining butter, chopped cabbage, garlic, salt, and black pepper to the skillet. Toss well to coat in the butter.

Cook the cabbage mixture, stirring occasionally, until deeply tender and caramelized on the edges, about 10 to 12 minutes.

Add the cooked egg noodles to the skillet with the cabbage. Toss everything together until well combined and heated through, adding a splash of reserved pasta water if needed. Taste and add more salt and pepper if desired.