In a soup kettle over medium heat, cook the bacon until it’s cooked through but not crispy about 7 minutes). Reduce heat to low. Remove bacon with a slotted spoon. Drain bacon fat, leaving one tablespoon in the soup kettle.
Add the oil and butter to the kettle. Once heated, add the leeks, carrots and celery. Season the vegetables with salt, white pepper, thyme and oregano. Increase the heat back to medium. Cook for 5-6 minutes (stirring and scraping up brown bits) or until the vegetables become tender. Add the garlic and cook another 2 minutes.
Add the flour, stirring to coat the vegetables. Cook for 3-4 minutes, but do not let it brown. Slowly add the chicken stock.
Add the cannellini beans, bacon, brussels sprouts and lemon juice. Bring to a boil and then reduce to a simmer. Cook for 20 minutes or until Brussel sprouts are tender.
Garnish with fresh parsley.
Note: Can be made up to 4 days prior to serving. If soup becomes too thick, add an extra cup of Chicken Stock.