Place the potatoes in a large pot and cover with cold water. Bring to a boil over high heat, then reduce to a simmer and cook until the potatoes are tender when pierced with a fork, about 15-20 minutes.
While the potatoes cook, peel the onions and slice them as thin as possible. Chop the pickles into small bits and set aside.
Once the potatoes are tender, drain them in a colander and carefully peel off the warm skins using a peeler or your fingers—peeling while still warm makes mashing easier and releases a lovely starchy aroma.
Transfer the peeled potatoes to a large mixing bowl and gently mash them with a fork or potato masher until mostly smooth with some small chunks remaining for texture.
Add the mayonnaise, vinegar, and mustard to the mashed potatoes, and stir until well combined and creamy. Taste and season with salt and pepper as needed.
Fold in the sliced onions, chopped pickles, and chopped dill, mixing evenly so every bite has a burst of tangy, crunchy goodness.
Let the potato salad sit for at least 30 minutes in the fridge to allow the flavors to meld and the textures to set, giving a refreshing aroma ready to serve.
Give the salad a gentle stir before plating, taste again, and adjust seasoning if needed. Serve cold or at room temperature for the best flavor and texture.
