Preheat the oven to 450F. Arrange garlic in a small dish or wrap in tin foil. Roast (you don't have to wait for the oven to heat up, just toss the garlic in) for 45 minutes until the top of the garlic bulb is brown and the bulbs are soft. Let cool until you can touch them.

While the garlic cools, slice and toast the bread any way you like. I toast it in a dry skillet over medium-high heat for 3 minutes or so on each side. A toaster or broiler works great too!

When the garlic has cooled, cut each bulb in half crosswise (halving each of the cloves), and squish the roasted garlic into a bowl. Add the olive oil and a sprinkle of salt, and mash with a fork until a paste forms.

Assemble the crostini by spreading the bread with a thin layer of the garlic mixture. Sprinkle with a bit more salt, and shave parmesan directly over top, if using.