Step 1: Cook the Eggs to Perfection. Place eggs in a single layer in a saucepan and cover with cold water by about an inch. Bring water to a rolling boil over high heat. Once boiling, immediately turn off the heat, cover the pan, and let sit for 9-10 minutes. While eggs cook, prepare an ice bath.
Step 2: Chill and Peel the Eggs. Transfer hot eggs to the ice bath and let cool completely for at least 5 minutes. Gently tap each egg on a hard surface to crack, then roll to loosen the shell. Peel eggs under cold running water for easier removal.
Step 3: Chop the Eggs. Once peeled, roughly chop the eggs to your desired consistency. Transfer the chopped eggs to a medium mixing bowl.
Step 4: Prepare the Dressing. In a small bowl, whisk together the mayonnaise, Dijon mustard, apple cider vinegar (if using), salt, black pepper, and optional pinch of sugar. Taste and adjust seasoning.
Step 5: Combine and Mix. Pour the dressing over the chopped eggs. Add the finely diced celery and red onion. Gently fold all ingredients together until well combined, being careful not to overmix.
Step 6: Taste and Adjust Seasoning. Taste the egg salad and adjust salt, pepper, mustard, or vinegar as needed to reach your preferred flavor profile. Chill for at least 30 minutes before serving for best flavor.