Heat the oven to 400 degrees. Slice the top off the head of garlic, drizzle with a little olive oil, wrap in foil, and roast for 30 minutes until soft. Set aside to cool.

Pat the beef dry and season with salt and pepper. Heat the olive oil in a Dutch oven over medium-high heat and brown the beef in batches until all sides are seared. Remove the beef and set it aside.

Add the onion, carrots, and celery to the same pot. Cook for 5 minutes until the onion softens. Sprinkle in the flour and stir for 1 minute to coat the vegetables.

Pour in the ale and beef broth, scraping the bottom of the pot to release any browned bits. Return the beef to the pot along with the potatoes.

Squeeze the roasted garlic cloves out of their skins and stir them into the stew. Add one rosemary sprig and bring everything to a simmer.

Cover the Dutch oven and cook on low heat for 2 hours, stirring occasionally, until the beef is fork-tender. Remove the rosemary sprig and add the remaining fresh rosemary leaves right before serving. Adjust salt and pepper to taste.