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1
Arrange a rack in the middle of the oven and preheat to 450 degrees F.
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2
In a dutch oven, combine the potatoes with enough water to cover them by 2 inches, bring the water to a boil, and boil the potatoes for 15 minutes, or until they are tender.
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3
Transfer the potatoes with a slotted spoon to a colander, reserving the cooking liquid, and force them through a ricer into a bowl. (or mash until smooth with no chunks).
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4
Add the butter, 1/4 cup of broth, the vinegar, and salt and pepper, to taste, and combine the mixture well.
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5
Bring the reserved cooking liquid to a boil. Coursely chop the kale leaves, add to water, and boil it for 10 minutes, or until it is crisp-tender.
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6
Drain the kale in the colander, refresh it under cold water, and press out the excess water.
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7
Stir the kale and 1/2 cup of the Swiss into the potato mixture and spread the mixture in a buttered casserole dish.
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8
In a large skillet brown the kielbasa over moderate heat and transfer it to a bowl with the slotted spoon.
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9
In the fat remaining in the skillet cook the onions over moderate heat, stirring, until they are golden. Stir them into the kielbasa.
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10
Scatter the kielbasa mixture on top of the potato mixture, sprinkle it with the remaining Swiss, and pour the remaining 1/4 cup broth on top.
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11
NOTE: The casserole may be prepared up to this point 1 day in advance and kept covered and chilled.
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12
Bake the casserole until heated through, about 20 minutes.
