Fill a large bowl with ice water and set aside. Bring a large pot of salted water to a boil. Add the green beans and cook until crisp-tender, 7 to 10 minutes. Drain and immediately transfer to the ice bath; let sit until cool, about 2 minutes. Drain and pat dry. Slice the green beans in half lengthwise.
Make the dressing: Whisk the creme fraiche, heavy cream, dijon and whole-grain mustard, and 1/2 teaspoon salt in a large bowl. Add the green beans and toss to coat. Drizzle with the vinegar and add the frisee and herbs; season with salt and pepper and toss.