Preheat oven to 400°F. Line a baking sheet with parchment paper.
Slice baguette in half. Set aside.
In a large bowl, mash together the softened butter, pesto, parmesan, garlic. Use a fork to mash the butter down and into the other ingredients. Mix until well combined.
Brush or spoon the pesto onto the inner cut halves of the bread. Place on the prepared baking sheet.
Bake at 400°F for 12-15 minutes, just until the bread has a light golden crust.
Slice the bread. Sprinkle just a few sea salt flakes over the pesto bread. Serve.