Heat the oven to 400°F (200°C). Slice 1/4 inch from the top of the garlic head, drizzle with olive oil, wrap loosely in foil, and roast for 30 to 35 minutes until very soft. Cool until easy to handle.
Squeeze the roasted cloves into a bowl and mash until smooth. Mix in the softened butter, grated fresh garlic, parsley, chives, Parmesan, salt, and pepper.
Increase the oven to 425°F (220°C). Slice the loaf in half lengthwise and place it cut-side up on a parchment-lined sheet pan. Spread the garlic butter evenly to every edge.
Bake for 8 to 12 minutes, until the butter is bubbling and the edges are golden. For a crispier top, broil for 30 to 60 seconds while watching continuously.
Rest for 2 minutes, garnish with extra herbs, cut into thick pieces, and serve warm.