From Vegetable Literacy by Deborah Madison, this was the recipe that taught me I like mustard greens! As Madison writes, you can use a mix of red and green mustards, or go with just one kind if you prefer.
8 heaping cups stemmed mustard greens (about 8 oz)
2 teaspoons roasted peanut oil
1 plump garlic clove, slivered
Few drops of soy sauce
A handful of roasted peanuts, coarsely chopped
Chop the mustard greens into large pieces and give them a rinse.
Heat the oil in a skillet over medium-high heat and then add the garlic. As soon as the garlic starts to sizzle, add the mustard greens and season with a few pinches of salt. Saute, turning the greens frequently, until the water from the leaves is largely gone and the leaves are tender. This should take about 5 minutes, depending on the plant. Add the soy sauce, cook for another minute, then toss with the peanuts and serve.
With soba: Toss the mustard greens with soba noodles and garnish with the peanuts
With smoke: Season the cooked greens with a few pinches of smoked salt
With tofu: Serve these garlicky greens with cubes of steamed tofu or golden friend tofu and season with red pepper flakes or a few pinches of shichimi togarashi (a Japanese seasoning blend that can be found at Japanese groceries or made at home)
With sesame: Instead of using peanut oil, cook the greens in light sesame oil, then toss with toasted sesame seeds and finish with a few drops of toasted sesame oil