Pierogi and Kielbasa Bake

Heat oven to 450 degrees F. Bring a large pot of water to a boil. Heat the oil in a large skillet over medium heat. Add the kielbasa and cook until browned on one side, about 3 minutes. Stir in the onion and cook, covered, stirring occasionally, until tender, 6 to 7 minutes. While the onion is cooking, boil the pierogies according to package directions; drain. Add the cabbage and cider to the onions and cook, tossing occasionally, until beginning to soften, about 4 minutes. Stir in the sauerkraut, mustard, and then the parsley. Arrange one-third of the pierogies on the bottom of a deep 8- by 8-inch baking dish, top with a third of the cabbage mixture (about 1 1/2 cups), and 1/2 cup cheese; repeat twice. Bake until the cheese melts, 8 to 10 minutes.