2 tbsp. butter
1 large onion, sliced or diced
1 tsp sugar

  • saute on low heat for 30 minutes, until well browned

1/2 cup red wine or dark beer
1 tsp thyme
1 tsp sage

  • add and bring to boil for 2 minutes

1 1/4 cups broth
1 tsp. Worcestershire sauce
1 tsp. balsamic vinegar
1/2 tsp. mustard
1/2 tsp salt
1/4 tsp. black pepper

  • add and simmer for 20 minutes

2 tsp. cornstarch
2 tsp. water
salt and pepper to taste

  • stir cornstarch into water, then add to gravy
  • whisk until smooth and combined

source: https://www.daringgourmet.com/onion-gravy/