In a small bowl, add the softened butter, ground mustard, and miso. Whip together until fully incorporated. Fold in the chives until evenly distributed. Taste and add salt to taste, if needed.
Bring a large saucepan filled halfway with water to a boil. Decrease the heat to a simmer and gently lower the eggs into the water one at a time, using a spoon. Cook for 5 - 7 minutes, depending on your egg yolk preference (I like my egg yolk runny, so I go with 5 minutes).
While the eggs are cooking, toast the bread. Slather with the butter mixture and slice into strips.
Prepare a bowl of cool water. Drain the eggs and gently add the eggs to the water to stop the cooking process. Once cool enough to handle, remove the eggs from the water. Serve immediately with toast soldiers.
To eat - using a spoon, tap the top of the egg all the way around and peel the shell. Scoop and dip the toast soldiers into the yolk. Enjoy!
Notes
If you don't have a soft boiled egg cup, don't worry! A shot glass works well. Or you can just peel the entire egg, slice it on a plate and then dip your soldiers.
Recipe by at https://hapanom.com/dippy-eggs-soldiers/