In a 6-qt. dutch oven, cook the bacon over medium heat, stirring occasionally, until lightly browned, about 5 minutes. Using a slotted spoon, transfer to a medium bowl. Season the lamb with salt and pepper. Working in 2 batches, add the lamb to the pot and brown on all sides, about 5 minutes per batch; transfer to the bowl with the bacon.
Add the onion, garlic and rosemary to the pot and season with salt and pepper. Cover and cook over low heat, stirring occasionally, until softened, 5 to 7 minutes. Add the broth, bring to a boil over medium-high heat and cook until nearly evaporated, about 5 minutes. Add the lamb, bacon and tomatoes to the pot and press a piece of parchment on top. Cover and cook over low heat until very tender, about 2 1/2 hours. Garnish each serving with a rosemary sprig.