Mushrooms Berkeley

¼ cup red wine

2 tablespoons Dijon mustard

2 tablespoons Worcestershire sauce

⅓ cup brown sugar

½ cup butter

1 sweet onion, halved and sliced

1 pound fresh mushrooms, halved

salt and ground black pepper to taste

Stir the red wine, mustard, Worcestershire sauce, and brown sugar together in a bowl until the sugar is thoroughly incorporated into the mixture; set aside.

Melt the butter in a saucepan over medium heat; cook and stir the onion in the melted butter until translucent, 5 to 7 minutes. Add the mushrooms, season with black pepper, and continue cooking and stirring another 3 minutes. As the mushrooms reduce in size and begin to brown, stir the wine mixture into the mushroom mixture. Simmer until hot, 1 to 2 minutes. Serve immediately.