1. Peel the salsify roots, keep them in cold water with lemon juice until all peeled.
2. Meanwhile, bring a sauce pan of water to boil with 2 tablespoon of white wine vinegar and salt.
3. Cut the salsify in 2 or 3 pieces to fit the pan. Simmer until tender. Remove from heat and leave to cool.
4. Sweat the onion with butter until translucent but do not colour.
5. Add the pancetta and garlic and cook for a few minutes.
6. Add the cream, bring to simmer and season to taste. Remove from heat.
7. Drain the salsify and cut diagonally 3cm long x 1cm thick. Add the salsify to the cream and toss together. Check seasoning.
8. Pour the mixture into a baking dish. There should be enough cream to just cover the salsify.
9. Sprinkle the top with parmesan and bake at 200°C until the top has turned golden.
10. Remove from heat and leave to cool slightly before serving.