Fill a large pot with water, stir in the salt and bring to a boil over high heat. Add the green beans and cook, until tender, about 5 minutes. Drain.
In a large skillet, melt the butter over medium heat. Add the pine nuts and cook, stirring often until golden brown, about 4 minutes. Stir in ¼ cup of the pesto. Add the green beans and toss until coated, about 2 minutes.
To serve, transfer the green beans to a plate, drizzle with the remaining ¼ cup pesto and sprinkle with flaky salt. Serve immediately.