Step 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.

Step 2

Add ramp bulbs to skillet; season with salt and cook, stirring occasionally, until translucent and tender, about 4 minutes.

Step 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.

Step 4

Purée ramp greens, ramp bulbs, half of pistachios, and remaining ⅔ cup oil in a food processor until very finely chopped. Add ½ 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.

Step 5

Return reserved pot of water to a boil; cook pasta, stirring occasionally, until al dente; drain, reserving ½ cup pasta water.

Step 6

Mix pesto, ¼ 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.

Step 7

Divide pasta among bowls. Top with more Parmesan and remaining pistachios.

Step 8

Do Ahead: Pesto can be made 2 days ahead. Cover with plastic wrap, pressing directly onto surface, and chill.