Preheat oven to 350 degrees.

Cut off the top third of the garlic with a sharp knife. Place the bulb in the middle of a piece of aluminum foil. Drizzle the bulb generously with olive. Season with salt and pepper.

Carefully wrap the foil around the garlic bulb. Bake the garlic until the cloves are soft and fragrant, about 30 minutes. Allow cloves to cool slightly, then gently squeeze them into a small bowl.

Melt the butter in a large pot over medium heat. Add the sliced fennel and cook until tender, about 5-7 minutes. Add the roasted garlic and cook for an additional 30 seconds.

Add the mussels to the pot. Pour the beer over the top, cover, and simmer until the shells begin to open, about 5-7 minutes. Discard any mussels whose shells do not open.

Pour the mussels and all their broth into a large bowl. Serve hot with a loaf of crusty bread.