Prepare an ice bath in a big bowl.

Bring a medium-sized pot of water to boil. The water level should be high enough to cover the eggs. Once boiling, carefully lower the eggs using a ladle. Boil for 7 minutes for medium soft boiled eggs or 10 minutes for hard boiled eggs. Then transfer eggs to the ice bath and let sit for 2 minutes. Peel the eggs.

Transfer the peeled eggs to a large bowl. Mash the eggs with a fork, then add sugar, salt, and pepper. Keep mashing until the eggs are in small pieces.

Add the mayonnaise (and milk if using hard boiled eggs). Mix everything together and adjust seasoning if needed.

Spread ½ tablespoon of butter evenly onto each slice of bread. Spread egg salad onto one slice of bread, place another slice on top, butter side down. Slice the crust off the bread. Assemble the other sandwich similarly and garnish with chives if using.

Cut the sandwiches in half and serve immediately.

Wrap each sandwich with plastic wrap and store in the fridge for up to 2 days.