Scrub the red potatoes and, if they are larger than 1.25 inches, halve or quarter so pieces are roughly 1–1.5 inches. Place potatoes in a large pot and cover with cold water by about 1 inch. Add 1 tablespoon salt. Bring to a boil over high heat, then reduce to a simmer and cook until potatoes are tender when pierced with a fork, about 12–15 minutes depending on size. Begin checking at 10 minutes to avoid overcooking.

Drain and cool slightly

When tender, drain potatoes in a colander and let them steam-dry in the colander for 3–5 minutes. While still warm (but cool enough to handle), transfer to a large mixing bowl and cut any larger pieces so all bite-sized pieces are uniform.

Make dressing

In a separate bowl, whisk together the sugar, whole grain or Dijon mustard, apple cider vinegar, lemon juice, and freshly ground black pepper. Slowly whisk in the olive oil to emulsify. Taste and adjust seasoning — add a pinch more salt if needed. The dressing should be bright, tangy, and slightly creamy.

Vegetables & herbs

Prep vegetables

While potatoes cook and cool, thinly slice the celery ribs into small half-moons, finely dice the red onion into small pieces (so the onion flavor distributes without overwhelming), finely chop the parsley and dill (if using), and thinly slice the scallions. Combine these prepared vegetables and herbs in a medium bowl.

Blanch onion (optional)

If you want a milder onion flavor, place the diced red onion in a small bowl and cover with cold water for 5 minutes, then drain and pat dry before adding to the vegetable mix.

Add-ins & finish

Combine potatoes and vegetables

Pour the dressing over the warm potato pieces and gently fold to coat so the potatoes absorb flavor. Add the prepared celery, red onion, scallions, parsley, dill (if using), and sweet pickle relish. Gently fold to combine.

Add mayonnaise and eggs

If using mayonnaise and chopped hard-boiled eggs, add them now. Start with 1/2 cup mayonnaise; fold it in and add more (up to 1/3 cup extra) only if you prefer a creamier salad. Gently fold in the chopped hard-boiled eggs so they remain in chunks rather than mashing.

Adjust seasoning and chill

Taste and adjust salt and pepper. Add the extra 1 teaspoon whole grain mustard if you want more mustard bite. Sprinkle the smoked paprika over the top for color and a touch of smoky flavor. Cover and chill for at least 1 hour to let flavors meld; salad can be served slightly warm as well, but chilling improves texture and flavor.

Serve

Before serving, give the potato salad a gentle stir and garnish with an additional sprinkle of chopped parsley or a little extra smoked paprika if desired. Serve cold or at room temperature.