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1
Cut the tofu into 3/4-inch cubes, then put them in a bowl. Dissolve 1 teaspoon of the salt in the 2 cups of hot water. Pour over the tofu; it should be just covered. Set aside for 15 minutes to season. Pour the water off, then transfer the tofu cubes to a non-terry dishtowel or double layer of paper towels placed atop a plate. Set aside to drain.
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2
Put the ginger, garlic, and onion in a food processor. Run the machine to yield a finely chopped texture, occasionally pausing to scrape down the sides. Transfer to a bowl and set aside. Reassemble the food processor (you don't have to wash it) for finely chopping the greens later.
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3
Rinse the mustard greens well, then coarsely chop, discarding the thick ribs. (If you are using braising mix, rinse, then coarsely chop the entire leaf because the ribs are tender.) Transfer to a 5- or 6-quart pot. Discard any root ends from the spinach, then rinse well. Coarsely chop the leaves and stems, then add to the pot of greens. To facilitate cooking, splash in a little water.
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4
Cover and cook over high heat for 5 to 7 minutes, until the greens have wilted and just cooked through. They will turn bright green and collapse to one-fourth to one-third of their original volume. To ensure even cooking, occasionally uncover the pot, stir, then replace the lid. When done, set aside to cool for 5 minutes.
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5
Transfer the greens to the food processor, discarding the residual liquid. Process to a rough yet finely chopped texture. Add 1/2 cup water (room temperature is fine) and pulse to blend together. Set aside.
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6
Heat the oil in a large nonstick skillet over high heat. Blot the tofu cubes dry, then panfry them in two batches for about 5 minutes, until light golden on 3 or 4 of the sides. Turn the tofu with chopsticks or a spatula during the frying. If the tofu violently sputters and spits, lower the heat slightly. Your aim is to add a bit of character and depth to the tofu, not crisp it all over-it will be soft or crisp in places. Transfer to a plate, leaving the oil behind, and set aside.
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7
Adjust the heat to medium-high, then add the mixture of ginger, garlic, and onion. Cook, stirring frequently, for about 8 minutes, until the mixture has browned and begun to caramelize. Add the cumin and chile and continue cooking for 1 to 2 minutes more, until the mixture is highly aromatic and richly browned.
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8
Lower the heat to medium, return the tofu to the skillet, and stir to combine well. Add the greens, stirring to combine. Add the remaining 1/2 teaspoon salt and cayenne. Cook for 2 to 3 minutes, moving the mixture frequently, until heated through. The greens will slightly darken.
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9
Let the mixture sit for a few minutes to meld the flavors. Taste and add salt or cayenne as needed. Stir in the butter, transfer to a communal bowl or individual plates, and serve.
