Mix yogurt and sour cream in a baking bowl until smooth. Season with salt, pepper and coriander.
Melt the soaked gelatine in the heated juice of a lemon. Stir into yogurt mixture and gently fold in whipped cream.
Line the baking dish with plastic wrap and spread out the slices of plain bread so that they extend 5 cm beyond the edge of the terrine.
Fill with alternating layers of yogurt-sour cream mousse and salmon slices until the tureen is full. Close with the overlapping smooth slices and refrigerate for at least 3 hours.
Before serving, invert the terrine, remove plastic wrap and cut the terrine into 2-cm slices with a very thin, sharp kitchen knife.
Serve with freshly toasted white bread and dry white wine.
Tip: Use creamy natural yogurt for an even finer result!