Preheat oven to 375°F.

Put the garlic, rosemary, and olive oil in a small ovenproof skillet and heat slowly until the oil just begins to simmer. Put the skilet in the oven and bake for 10 minutes. Turn the cloves over in teh oil and bake for 10 minutes longer. Remove from the oven and let cool for 15 minutes.

Remove the garlic cloves from the oil (reserve the oil) and mash them to a paste with a knife. Take half the leaves off the rosemary sprig and finely mince them. In a bowl, combine the garlic paste, minced rosemary, and butter and stir until smooth.

Cut the baguettes in half widthwise, then lengthwise. Spread the cut sides with the seasoned butter and drizzle with a little of the oil used to bake the garlic. Arrange the halved baguettes on a baking sheet and sprinkle with the Parmesan, if using.

Bake until the baguettes begin to crisp, about 15 minutes. Cut into 2-inch-wide slices and serve immediately.