This hearty main course pairs lamb beautifully with roasted new potatoes. To save yourself a step, have your butcher prepare the meat.
In a large bowl, combine lamb, ¼ cup olive oil, rosemary, garlic, and bay leaves. Place in refrigerator two hours or overnight.
In a large Dutch oven over medium-high heat, add remaining olive oil. Remove lamb from marinade (shake off excess) and sear in the hot pan to brown on all sides. Do not crowd the pan; if necessary, work in batches. Remove lamb to a plate and tent with foil to keep warm. Lower heat to medium and add onion; cook until softened. Raise heat to medium-high, add wine, and use the liquid to scrape up the browned bits on the bottom of the pan. Add tomatoes and paste and stir well. Return lamb to the pan.
Bring the liquid to a boil, then lower temperature to simmer and cover the pan. Cook 35 to 45 minutes, stirring every 10 minutes or so. Remove lid; raise temperature to high and reduce liquid by half. Season with salt and pepper and add a pinch of red pepper flakes. Remove bay leaves before serving.