1.Preheat oven to 220°C, (200°C fan-forced). Grease 2 oven trays; line with baking paper.
2.Combine the water and butter in a medium saucepan; bring to the boil. Add flour; beat with a wooden spoon over a medium heat until mixture comes away from base of pan. Transfer pastry to a medium bowl; beat in two of the eggs, one at a time. Whisk remaining egg with a fork; beat enough of the egg into the pastry until it becomes smooth and glossy, but still holds its shape.
3.Beat in the grated gruyere or swiss cheese, olives and some freshly ground black pepper.
4.Drop tablespoonfuls of the batter onto the oven trays. Bake for 10-15 minutes or until puffed and lightly golden, then reduce oven temperature to 180°C (160°C fan-forced) and bake for a further 10-15 minutes. Sprinkle with the grated parmesan. Serve warm.