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1
Heat 1 Tbsp. oil in a large skillet over medium-low. Cook guanciale, tossing often, until browned and crisp, 10-15 minutes. Transfer to a small bowl with a slotted spoon. Pour off all but 2 Tbsp. fat from skillet.
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2
Add ramp bulbs to skillet; season with salt and cook, stirring occasionally, until translucent and tender, about 4 minutes.
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3
Meanwhile, blanch ramp greens in a large pot of boiling salted water until wilted, about 10 seconds. Using a slotted spoon, transfer to a bowl of ice water (save pot of water). Drain, squeeze out excess liquid, and coarsely chop.
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4
Puree ramp greens, ramp bulbs, half of pistachios, and remaining 2/3 cup oil in a food processor until very finely chopped. Add 1/2 cup Parmesan and process until pesto is almost smooth. Pulse in a little more oil if sauce is too thick; season with salt and pepper.
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5
Return reserved pot of water to a boil; cook pasta, stirring occasionally, until al dente; drain, reserving 1/2 cup pasta water.
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6
Mix pesto, 1/4 cup pasta water, and butter in a large bowl. Using tongs, transfer pasta to bowl and add guanciale; toss vigorously, adding more cooking liquid as needed until pasta is glossy and well coated with sauce. Taste and add more salt if needed.
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7
Divide pasta among bowls. Top with more Parmesan and remaining pistachios.
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8
Pesto can be made 2 days ahead. Cover with plastic wrap, pressing directly onto surface, and chill.
