1.
First, prepare the mayonnaise: place the egg, salt, lemon juice and
extra virgin olive oil in the jar of an immersion blender. Insert the blender arm all the way in and beat for a few seconds. As the mixture begins to emulsify, gradually lift up the arm. Repeat the operation for a few seconds until the sauce is smooth.
2.
Slice the hardboiled eggs into cubes and put them in a bowl. Mix them with the mustard, mayonnaise, oregano and diced red onion. Smash everything with a fork to form a paste.
3.
Lay the smoked salmon on a slice of bread,* and top it with some of the egg mixture. Close the sandwich with another slice of bread. Repeat the operation for the other 3 sandwiches.
*Toast the bread if you like and, for more flavor, add a splash of
extra virgin olive oil.