In large, heavy bottomed saucepan, add 1/4 cup (60 mL) olive oil and sauté onion, rosemary, bay leaves, 3 sprigs thyme, and garlic for 3 minutes over medium heat. Add leek and continue to sauté until all contents are soft, about 10 minutes. Add beans and water to cover, about 5 to 6 cups (1.2 to 1.4 L). Increase heat to bring to a boil, then reduce to low to simmer slowly. Cook for 1 to 2 hours, until most cooking liquid has evaporated and garlic and onions have melted into a silky sauce. Season with salt and pepper and keep warm while preparing mushrooms.
