Step 1

Heat butter and oil in a large cast iron dutch oven over medium-high heat. Add onion and sugar and stir to combine. Cook for about 10 minutes, until onions are starting to brown. Give a good stir and reduce heat to medium. Continue to cook until onions are brown and caramelized, almost jammy (see pic), about an hour, stirring every 10 minutes. Be patient here! You want those onions to be brown and rich with flavor!

Step 2

Meanwhile, cook tortellini according to package directions and set aside.

Step 3

When the onions are caramelized, but not quite jammy yet (see pic), add the garlic and mushrooms. Give a good stir and cook another 10 minutes. Add the red wine vinegar, and cook about 5 minutes, stirring occasionally.

Step 4

Remove the sauce from the heat and toss in the tortellini. Season with salt and pepper and add most of the parsley, leaving some for serving. Toss all together and serve, topping with additional fresh parsley.