Cook the pasta just right: Bring a large pot of well-salted water to a boil. Add elbow macaroni and cook until just past al dente, about 1–2 minutes longer than package al dente time. You want it tender but not mushy.
Cool it quickly: Drain and rinse the pasta under cold water until cool.
Shake off excess water well. This stops the cooking and prevents clumping.
Make the dressing: In a large bowl, whisk together mayonnaise, sour cream, apple cider vinegar, Dijon, sugar, celery seed, garlic powder, 1 teaspoon kosher salt, and 1/2 teaspoon black pepper. Taste and adjust sweetness, tang, and salt.
Prep the mix-ins: Finely dice celery, bell pepper, and onion.
Chop pickles (or measure relish). If using, chop hard-boiled eggs and thaw peas.
Toss it together: Add cooled macaroni to the bowl of dressing. Fold in celery, bell pepper, onion, pickles/relish, eggs, and peas.
Stir gently until evenly coated.
Chill for best flavor: Cover and refrigerate at least 1 hour, ideally 2–4 hours. The pasta will absorb some dressing and the flavors will meld.
Adjust before serving: Give it a stir. If it seems a bit dry, add a spoonful of mayo or a splash of milk to loosen.
Taste and adjust salt and pepper.
Finish and serve: Sprinkle with paprika and fresh herbs if you like. Serve cold or slightly chilled.