1. Cook bacon in 12-inch skillet over medium-high heat until beginning to render fat, about 1 minute. Add onions and sugar and cook, stirring occasionally, until bacon is crisp and onions are light brown, about 8 minutes. Using slotted spoon, transfer onions and bacon to medium bowl. Reserve 1 tablespoon bacon fat in small bowl; discard remaining fat. Add 1/4 cup port to now-empty skillet and return to medium-high heat; simmer about 30 seconds, scraping up any browned bits with wooden spoon. Pour port into bowl with bacon and onions; wipe out skillet with paper towels.

2. Heat reserved bacon fat in now-empty skillet over medium-high heat until shimmering but not smoking. Add mushrooms and cook, stirring occasionally, until mushrooms release liquid, about 5 minutes. Increase heat to high and cook, stirring occasionally, until liquid has completely evaporated and mushrooms start to brown, about 8 minutes longer. Add butter, reduce heat to medium, and continue to cook, stirring once every minute, until mushrooms are dark brown, about 8 minutes longer. Add bacon/onion mixture and remaining 1/4 cup port; cook, stirring frequently, until liquid has evaporated and mushrooms are glazed, about 2 minutes. Stir in parsley and season with salt and pepper to taste. Transfer to serving dish, sprinkle with blue cheese (if using), and serve.

Serves 4