Bring a large pot of well-salted water to a boil. Cook pasta until 1 minute shy of al dente, according to the package directions. Drain, reserving 1/2 cup of pasta water.
Meanwhile, heat oil in large sauté pan over medium heat; add scallion whites and a pinch of salt and cook until soft, 3 minutes. Add 1/4 cup water and all but 1/4 cup corn; simmer until corn is heated through and almost tender, 3 to 5 minutes. Add 1/4 teaspoon salt and 1/4 teaspoon pepper, transfer to a blender, and purée mixture until smooth, adding a little extra water if needed to get a thick but pourable texture.
Heat the same skillet over high heat. Add butter and let melt. Add reserved 1/4 cup corn and cook until tender, 1 to 2 minutes. (It’s O.K. if the butter browns; that deepens the flavor.) Add the corn purée and cook for 30 seconds to heat and combine the flavors.
Reduce heat to medium.
Add pasta and half the reserved pasta cooking water, tossing to coat. Cook for 1 minute, then add a little more of the pasta cooking water if the mixture seems too thick. Stir in 1/4 cup of the scallion greens, the Parmesan, the herbs, the red pepper flakes, 1/4 teaspoon salt and 1/4 teaspoon pepper. Sprinkle with fresh lemon juice to taste. Transfer to warm pasta bowls and garnish with more scallions, herbs, a drizzle of olive oil and black pepper.
