1 cup butter, divided
2 large onions, chopped
2 small heads cabbage, cored and cut into 1-inch pieces
salt and ground black pepper to taste
1 tablespoon water, or as needed (Optional)
Preheat oven to 300 degrees F (150 degrees C). Fill a large pot with lightly salted water and bring to a rolling boil. Stir in egg noodles and return to a boil. Cook noodles uncovered, stirring occasionally, until tender but still slightly firm, about 5 minutes. Drain well. Melt 1/2 cup butter in a large skillet over medium-low heat; cook and stir onions until translucent, 5 to 10 minutes. Cook and stir remaining butter and cabbage into onions until cabbage is softened but not browned, 5 to 8 more minutes. Season with salt and black pepper. Place cooked noodles and cabbage mixture in a large roasting pan and stir gently to combine. Sprinkle with more salt and black pepper if desired. Bake in the preheated oven until golden brown on top, 30 to 40 minutes.