3. In a bowl, mix snapper, cucumber, potato, pepper, shallot, herbs and zest. Add mayonnaise and combine. Refrigerate until needed.
4. For the sauce topping, mix sour cream, horseradish, juice, cayenne and herbs in a small bowl.
5. Place a 6-7cm pastry ring on a plate and fill with a quarter of the snapper mix, pushing it down gently. Smooth the top. Remove the ring gently, running a sharp knife around the circumference if necessary. Repeat for the rest of the mixture. Place a dollop of sauce on the top of each.