Red wine onions is a heady mix of red onions, red wine, a bit of brown sugar, and chile pepper flakes cooked low and slow. So incredibly jammy and unforgettable.
In a large skillet over medium heat, warm the olive oil. Add the onions and cook, stirring occasionally, until softened, about 15 minutes.
Sprinkle the onions with the brown sugar, salt, and red pepper flakes, and stir. Add the red wine, bring to a boil, and then reduce the heat to maintain a steady simmer.
Continue cooking, stirring occasionally, until most of the liquid has evaporated and the onions are collapsed and caramelized, 40 to 60 minutes more. Taste and adjust the seasoning as needed.
Use immediately or cover and refrigerate for up to 10 days, or freezer for up to 2 months.