Steps
- Bring 4in / 10cm of water to a boil in a saucepan. Lower in 6 eggs and boil for 8 minutes.
- Cool the eggs in cold water for 10 minutes, then peel. Crush with a fork and mash finely with a potato masher.
- Stir in 2 tablespoons of whole-egg mayonnaise, 2 teaspoons of Dijon mustard, and 2 teaspoons of finely chopped chives.
- Add ½ teaspoon of black pepper and ⅛ teaspoon of kosher salt. Mix gently until creamy.
- Spread ¼ cup of softened salted butter over 8 slices of soft white sandwich bread. Fill half the slices edge to edge with egg; close with the rest and cut into rectangles.