Bring a large pot of well-salted water to a boil. Cook pasta until 1 minute shy of al dente. Drain, reserving 1/2 cup pasta water.

Heat olive oil in a large sauté pan over medium heat. Add scallion whites with a pinch of salt and cook until soft, about 3 minutes. Add 1/4 cup water and all but 1/4 cup of the corn kernels. Simmer until corn is heated through, 3 to 5 minutes. Season with salt and pepper, then transfer to a blender and purée until smooth.

Wipe the skillet and return to high heat. Add butter and let it melt. Add the reserved 1/4 cup corn kernels and cook until tender, 1 to 2 minutes. Add the corn purée and cook for 30 seconds.

Reduce heat to medium. Add the pasta and half the reserved pasta water, tossing to coat. Cook for 1 minute, adding more pasta water if needed. Stir in scallion greens, Parmesan, basil, and red pepper flakes. Finish with a squeeze of lemon juice and serve immediately.