1. Bring 600 ml water, 100 g butter and a pinch of salt to the boil, add 350 g flour, mix well over heat till it leaves the pan clean, then allow to cool.
2. Add 6 eggs one by one, mixing thoroughly, 50 g Parmesan and 150 g diced Gruyere cheese.
3. Mould into 50 pieces using two tablespoons and golden deep fry at 190°C for 5 minutes.