Chestnut Linguini, Caramelized Onion

This came together so nicely tonight I had to write it down. I will take full credit for this combo. Thank you.

250 gr chestnut tagliatelle
1 onion, 12 shallots, 6 garlic cloves sliced thinly
a few rosemary needles (or thyme)
12 black peppercorns
1 bay leaf
2 tblsp white port
maldon sea salt
EVOO
1 tblsp butter
parmesan (optional)

1. put onion, shallot and garlic in big pan with EVOO, rosemary, pepper, bay leaf, salt
2. confit and caramelize for 3-4 hours on super low heat; about one hour in add the port
3. toward the end put lid on pan for quicker caramelization (around 20-30 mins)
4. set aside until needed and reheat if necessary
5. boil pasta, add 2 tblsp of pasta water to onion mixture to loosen
6. drain pasta and add to pan with butter
7. serve with grated parmesan, if you like