Boil the eggs: Place eggs in a pot with cold water and bring to a rolling boil. Cover and remove from heat, letting them sit for 12 minutes.

Cool the eggs: Prepare an ice bath and transfer the eggs to cool for 10–15 minutes. Once cool, gently crack the shells and refrigerate overnight.

Prepare the pickling liquid: Combine apple cider vinegar, water, sugar, salt, and sliced beets in a saucepan. Bring to a boil and cool to room temperature.

Pickle the eggs: Peel the eggs and place them in a jar. Pour the brine over the eggs, ensuring they are submerged, and refrigerate for at least 4 hours.

Make the filling: Slice eggs in half, scoop out yolks into a bowl, and mix with mayonnaise, vinegar, and mustard until smooth.

Fill the egg whites: Pipe or spoon the yolk mixture into egg whites and garnish with chives before serving cold.