Keep each scallion bunch separate.

Chop one bunch of scallions into roughly 1 ½–inch pieces.

Chop another into ½-inch pieces.

Finely slice then mince the remaining bunch.

Heat a large pot or Dutch oven over medium-high heat. When it’s very hot, add 1 tablespoon oil.

When the oil is shimmery, add the large-sized scallion pieces. Toss a few times and sprinkle with salt. Leave pieces to cook for 3 minutes, until they begin to char.

Add the medium-sized scallion pieces to the pan. Stir and season with another pinch of salt. Lower the heat to medium and cook for another 3 minutes, stirring a few times, until soft.

Add the minced scallions to the pan. Stir and season with another pinch of salt. Lower the heat to the lowest possible setting, then add the remaining 4 tablespoons olive oil. Cook for about 2 minutes, stirring once or twice. Then turn off the heat. Stir in the red pepper flakes.

Bring a separate pot with the 7 cups of water to boil.

Add a few pinches of Kosher salt and add the bucatini. After a moment, gently nudge it down with a wooden spoon as needed, until all the noodles are submerged. Set a timer for 9 minutes and boil noodles, stirring occasionally to prevent sticking, until just al dente.

At minute 7 of the pasta's cooking time, turn on the heat under the scallion sauce to the lowest setting and give the scallion oil a stir.

Use tongs to transfer the bucatini to the pot with the scallions and oil.

Add 1/3 cup pasta water and continuously and vigorously stir the pasta to form an emulsified sauce (about 2 minutes).

Incrementally add more water, if necessary.

Turn off the heat and plate the bucatini. Top with more red pepper flakes and flaky sea salt.