1. In a tall jar, put hard-boiled eggs, drained tuna (if it is in olive oil - add all the oil), capers, lemon juice, salt and pepper.
2. Insert the hand blender into the bottom and blend everything until a velvety smooth mass. If using tuna in your juice, add olive oil a little at a time while whisking.
3. If the sauce seems too thick, add a teaspoon of cold water and blend again.