Chop Onion in half cut through about 3 times then rough chop.

Melt butter in pot sautee onion for 5 min on med heat

add flour continue to cook stiring often to make a roux

add White wine stirring constantly

add Chicken stock continue stirring continue to cook untill sauce thickens if sauce is too thick add more chicken stock or white wine to thin out

Then add Thyme salt and pepper to taste

Add brown sugar and course mustard

Finish by adding cream and cook for additional 5 min