Prepare the eggs: Place eggs in a single layer in a large pot. Cover with cold water by about 1 inch.
Add a pinch of salt if you like (helps prevent cracks).
Boil and rest: Bring to a rolling boil over medium-high heat. Once boiling, cover, turn off the heat, and let sit for 12 minutes for fully set yolks.
Ice bath: Transfer eggs immediately to a bowl of ice water. Chill at least 10 minutes.
This helps with peeling and stops overcooking.
Peel carefully: Gently crack each egg and peel under cool running water. Pat dry with paper towels.
Halve and scoop: Slice eggs lengthwise. Pop yolks into a medium bowl and place whites on a platter.
Mash the yolks: Use a fork to break up yolks until fine and crumbly.
The finer the mash, the smoother the filling.
Mix the filling: Add mayonnaise, mustard, and vinegar. Stir until very smooth. Season with salt and pepper.
Taste and adjust—more mustard for zip, more mayo for creaminess, or a splash more vinegar for tang.
Fill the whites: Spoon the mixture into the egg white hollows, or transfer to a zip-top bag, snip a corner, and pipe for a cleaner look.
Garnish: Dust lightly with paprika. Add chives or dill if using.
Chill: Refrigerate at least 20 minutes before serving so flavors settle and the filling firms up slightly.