Place the peeled potato chunks 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 but still hold their shape, about 15-20 minutes. You should see gentle bubbling and the potatoes feeling soft when pierced with a fork.
Drain the potatoes in a colander and carefully transfer them to a mixing bowl while still warm. The steam will escape with a faint hissing sound, filling the air with a subtle earthy aroma. Let them sit for just a minute to cool slightly but remain warm enough to absorb the dressing.
Gently mash the potatoes with a fork or potato masher, aiming for a chunky but mostly smooth texture. You want some pieces to hold their shape, creating a hearty base for the salad.
Add the mayonnaise, finely chopped red onion, chopped celery, Dijon mustard, and lemon juice to the mashed potatoes. Use a spoon or spatula to fold everything together, ensuring the ingredients are evenly distributed and coated in the creamy dressing. The mixture should be well combined but not overmixed to avoid turning mushy.
Season the mixture generously with salt and freshly ground black pepper. Taste and adjust the seasoning, adding more lemon juice or salt if needed to brighten and enhance the flavor.
Transfer the potato salad to a serving bowl, cover loosely with plastic wrap, and refrigerate for at least an hour. This resting time allows the flavors to meld and develop further.
Before serving, give the salad a gentle stir, taste once more, and squeeze a little extra lemon juice if needed. Serve chilled for a refreshing, creamy potato salad with a satisfying crunch and zing.
