Drain the cooked potatoes in a colander and rinse under cold water just until cool enough to handle but still warm. Quarter the potatoes, transfer to the sauce, and toss to coat. Add the celery, scallions (reserving some for garnish), and chives, and toss lightly to combine. Taste and season with more kosher salt and black pepper as needed. Top with the blue cheese and reserved scallions. Serve warm or at room temperature.