In a medium saucepan, saute the onions in the butter until tender.
Stir in the white wine, splash of whiskey and the mustards. Cook for 5 minutes or so.
Stir in the broth and thyme.
Reduce the heat and allow the liquid to reduce about half.
Stir in the cream and season with salt and pepper.
Continue to simmer over low heat until the desired consistency is reached. Add more broth, cream or mustard as needed. Season to taste with salt and pepper.