Prep. time: A few minutes
Waiting time: 1 hour
Cooking time: None

1. Soak the bread in cold water, remove the crusts and drain, squeezing well to form a fairly dry paste (about 500 ml or 2 cups).
2. Finely chop the onion, then purée in a blender, food processor or mortar;
3. in a bowl, combine the puréed onion, fish egg caviar and a quarter of the soaked bread; beat with a whisk or an electric mixer, evenly but not on too high a speed.
4. As if making a thick (but not stiff) mayonnaise, slowly drizzle in the oil while whisking constantly - start with vegetabe oil ; add the lemon juice and the remaining soaked bread. Finish with olive oil.
5. When all the ingredients are well-combined, whisk gently for 5 minutes. Season with white pepper. Let rest in the refrigerator for at least an hour. Serve cold.