Cut the potatoes into 1 ½" to 2" chunks (with the peel left on). Bring a medium pot of water to a boil. Add the potato pieces and eggs (in the shell) to the water and set to a light boil for 15 minutes. If after 15 minutes the potatoes are not tender when pierced with a fork, then remove the eggs and continue boiling the potatoes for a few minutes more. When finished drain and run cool water over top of the eggs and potatoes.

Meanwhile, dice the celery and onion and add to a large mixing bowl. In a separate smaller bowl, whisk together the sour cream, mustard, melted butter, salt, paprika, and pepper. Set aside.

Dice the cooked potatoes into smaller ½" pieces and add to the large bowl. Peel and dice the eggs (I use one of these slicers to cut the egg longways and then crossways for a quick dice) and add to the large bowl. Pour the sour cream mixture over top and toss to combine. Serve immediately or refrigerate for up to 5 days.