Cook potatoes in boiling salted water for 12 minutes or until tender; drain and cool slightly.
While potatoes are cooking, prepare dressing. In a small bowl, whisk together mayonnaise, Creole or spicy brown mustard, red wine vinegar, horseradish, salt, thyme, garlic powder and ground red pepper. Set aside.
In a medium bowl, combine cooled potatoes, egg, onion and dressing. Toss gently. Serve at room temperature or chilled.