Pat the lamb dry and season it with salt and pepper. Toss the chunks with the flour until lightly coated.
Heat the olive oil in a large skillet over medium-high heat. Brown the lamb in batches for 3 to 4 minutes per side, then transfer it to the slow cooker.
Add the onion and garlic to the same skillet and cook for 2 minutes until softened. Scrape everything into the slow cooker.
Add the potatoes, carrots, beef broth, and rosemary sprigs to the slow cooker. Stir gently to combine.
Cover and cook on low for 7 to 8 hours until the lamb is fork-tender and the potatoes are soft.
Remove the rosemary sprigs before serving. Taste and adjust salt and pepper if needed.