Carefully add the eggs to a pot of water, large enough for the eggs to have space to not knock into each other.
Bring the water with the eggs to a boil. (Do not walk away- watch for the water to start to boil or the eggs will over cook!)
When the water starts to boil, start a timer for exactly 3 minutes. If the water is boiling too intensly and the eggs are moving too much around, bring it down to a lower boil.
Carefully remove the eggs using a slotted spoon from the water, and set aside.
As soon as the eggs are cool enough to handle, peel the eggs.
Meanwhile, toast the bread. Spread each slice with 1/2 tbs of butter, then 1/2 tbs of whole grain mustard.
Place each egg on the center of each toast and slice the eggs down the middle, and then across, for 4 quarters. Be careful not to slice through the toast.
Sprinkle with dill, kosher salt & pepper. Finish with a sprinkle of fleur de sel (sea salt.)