Heat a large pot over medium-low heat and add the olive oil and butter. Add the leeks, salt, pepper and crushed pepper flakes and toss well to coat. Cook, stirring every few minutes, until the leeks begin to brown, about 20 to 25 minutes. Once the leeks are starting to brown, stir in the brown sugar and cook for another 10 minutes until they are super caramelized. Stir in the roasted garlic. Increase the heat slightly to medium and add the wine. Stir to combine, then cook for a few minutes until most of the wine cooks off. Pour in the stock and stir. Bring the soup to a boil, then reduce to a simmer and cook for 15 minutes.