2 1/2 lb. russet potatoes, peeled and quartered

Salt and freshly ground pepper, to taste

8 tbs. (1 stick) unsalted butter

3/4 cup milk

4 bacon slices, cut into 1/2-inch dice

4 large shallots, thinly sliced

1 large leek, white and light green portions, halved lengthwise, rinsed well and thinly sliced

1 bunch curly kale, about 3/4 lb., stemmed and coarsely chopped

1 small head napa cabbage, about 1 lb., cored and coarsely chopped

1/8 tsp. mace or freshly grated nutmeg

Put the potatoes in a large pot, add water to cover the potatoes by 2 inches and generously salt the water. Bring to a boil over medium-high heat, reduce the heat to medium and cook until the potatoes are tender when pierced with a knife, about 15 minutes. Drain well in a colander.
Meanwhile, in a small saucepan over low heat, combine the butter and milk and heat until the butter melts and the mixture is hot, 8 to 10 minutes.
Set a potato ricer over a large bowl and press the potatoes through in batches. Fold in the milk mixture in two additions. Season with salt and pepper. Cover the bowl with aluminum foil and set over a large saucepan of barely simmering water to keep warm.
Heat a heavy pot or Dutch oven over medium heat until hot. Add the bacon and cook, stirring occasionally, until browned and crisp, about 5 minutes. Using a slotted spoon, transfer the bacon to a paper towel-lined plate. Set aside.
Pour off all but 3 Tbs. of the fat from the pot. Return the pot to medium heat, add the shallots and leek and cook, stirring occasionally, until softened, about 5 minutes. Add the kale and toss just until wilted but still bright green, about 3 minutes. Add the cabbage and toss until tender-crisp, about 8 minutes. Sprinkle with the mace and the bacon, and season with salt and pepper. Stir the potatoes into the cabbage mixture and serve warm.