Sandwich telur

Bahan-bahan (4 porsi)

• 6 soft boiled eggs (, at room temperature (Note 1))
• 1 tbsp whole egg mayonnaise ((S&W brand best, Note 2))
• 2 tsp dijon mustard
• 2 tsp finely chopped chives ((sub green onion))
• 1/2 tsp black pepper
• 1/8 tsp cooking/kosher salt ((yes really, that's all!))
• 8 slices soft white sandwich bread ((Note 3))
• Soft salted butter (, for spreading on bread)