Cut the potatoes into bite-size or slightly larger pieces.
Boil the potatoes for 15-20 minutes, just until the point where you insert a fork and the potato falls off (overcooking can leave you with mashed potato salad).
While the potatoes are cooking, mix the mayonnaise, mustard, and onion.
Prepare the vegetables and stir them into the mayonnaise mixture.
Drain the potatoes, rinse with cold water, and fold them into the vegetables along with the optional eggs. Serve warm.
Notes
This salad tastes best warm, so serve it right away or remove from the fridge half an hour before serving.
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