Add potatoes to a large pot with enough cold water to just about cover them. Mix in 2 tsp salt then bring to a boil & cook until the potatoes are fork tender (10 or so mins once boiling). Be careful to not over-boil them or they'll turn to mush. Drain (don't rinse) and leave to steam dry until completely cool (important!).
Meanwhile, in a mixing bowl combine mayo, sour cream, lemon juice, cajun seasoning, mustard & parsley. Check for spice & seasoning and adjust with hot sauce (if you want it spicier) and more salt & pepper to taste.
Add cooked & cooled potatoes to a large mixing bowl. Place a wire rack over the top and press through the hard-boiled eggs. Add spring onion then pour in dressing. Give it a good toss then preferably pop in the fridge for at least an hour to give chance for the flavour to marry together & soak into the potatoes.
Add paper towels over the sliced onion & press down to remove some moisture. Heat up 1-2" of oil in a heavy pot pan to around 120C/250F. Add in the sliced onion until deep golden and visibly crispy. Remove with a slotted spoon and rest on paper towels. Sprinkle a pinch of salt over them as they cool.
Serve potato salad with a few pinches of smoked paprika & crispy onions on top.
