Put the potatoes in a large pot and add water to cover; season with salt. Bring to a boil, then reduce the heat and simmer until tender, about 12 minutes. Drain and let cool.
Combine the mayonnaise, sour cream, parsley, chives and tarragon in a blender. Add the anchovies, garlic, capers, lemon juice, ½ teaspoon salt and a few grinds of pepper; puree until smooth.
Combine the potatoes, hard-boiled eggs, bacon, scallions and celery in a large bowl. Add about 1 cup of the dressing and toss to coat; season with salt and pepper.