Cook Mafalda according to package directions, drain well
Meanwhile, melt 1 tablespoon of butter in a large heavy pan on low
Add onion, red pepper flakes and ½ teaspoon of salt to the pan and stir to coat onions
Cook onions on low, stirring frequently, until onions start to caramelize ~10 minutes
Stir in 1 tablespoon of butter, mushrooms, thyme and garlic
Continue cooking on low stirring until mushrooms are tender and browned ~7 minutes
Add in the final tablespoon of butter and vinegar and allow butter to melt
Pour in cream and heat until cream starts to lightly bubble
Mix in ¼ cup of parmesan and stir until fully melted
Add drained pasta to the pan and toss pan to coat mafalda
Serve with more parmesan and fresh parsley if desired