2. Mix sour cream, tarragon, capers, add salt and Tabasco to taste.
3. Cut the fish into strips.
4. Peel the avocado, cut into slices of medium thickness and pour generously with lemon juice.
Place a layer of avocado on top of the fish in a cooking ring. Alternate layers, top off with avocado and top with sour cream sauce. You can decorate with caviar.