Place the garlic in a food processor and process until finely chopped. Add the
bread to the chopped garlic and process to crumbs, add the mashed potato,
cayenne pepper and saffron and process. With the motor running add 1 tablespoon
of the olive oil, 1 tablespoon fish stock and the egg yolk. Drizzle in the
remaining olive oil in a slow steady stream until a mayonnaise forms, then
add the remaining fish stock. Transfer to a bowl and serve immediately or
plastic wrap and refrigerate until required.