Boil the potatoes with skins on for at least 30 minutes. Potatoes are done when you can easily stick a fork through the potatoes to their center. Drain the water from the pot and allow the potatoes to naturally cool to room temperature.
Peel the skins off the potatoes. Slice into chunks of whatever size/shape you're comfortable with. I like to slice the potato into 1/2-inch wide sections; then cut those up into chunks. Place these potato chunks into a large mixing bowl, salting to taste as they are added in layers.
Add the relish and onion to the bowl of potato chunks. Don't combine yet.
In a separate mixing bowl, combine mayonnaise, sour cream, mustard and sugar. Add the rosemary and optionally a few dashes of poppy seeds. Hand-whip until the color stabilizes. This is the potato salad dressing.
Add the dressing to the potato chunk mixture and stir the potato salad gently until all the potatoes are covered with the dressing.
Move the finished potato salad into a serving bowl. Note: This step is mainly intended for presentation purposes. You can leave the potato salad in the mixing bowl if you have nobody to impress.
Optional: Slice up the boiled egg and place the slices on top of the potato salad. Sprinkle paprika on top of everything.