Remove butter from the refrigerator at least 15 minutes before starting so it is softened. In a medium bowl, combine the softened butter and olive oil and mash together with a fork until smooth and spreadable.

Prepare garlic and herbs

Peel and finely mince the garlic cloves. Chop the fresh parsley finely. Add the minced garlic and chopped parsley to the butter mixture. Stir in the grated Parmesan (if using), salt, black pepper, and red pepper flakes (if using). Taste and adjust seasoning; the mixture should be garlicky and well seasoned.

Assemble Bread

Slice the loaf

Preheat the oven to 400°F (200°C). Place the baguette on a cutting board. Using a serrated knife, slice the loaf in half lengthwise so you have two long halves with exposed crumb.

Spread garlic butter

Use a spatula or butter knife to spread the garlic butter mixture evenly across the cut surfaces of both halves, making sure to get butter into nooks and across the edges. If using shredded mozzarella for cheesy garlic bread, reserve it for the next step.

Optional cheese topping

If making cheesy garlic bread, evenly sprinkle the shredded mozzarella over the buttered halves, pressing lightly so it adheres.

Bake & Finish

Bake

Place the buttered halves on a baking sheet, buttered sides up. Bake in the preheated oven for 8–12 minutes until the butter is melted and the edges begin to brown. If you added mozzarella and want it bubbling and golden, switch the oven to broil for 1–2 minutes at the end—watch closely to prevent burning.

Garnish and serve

Remove the garlic bread from the oven. If using, scatter torn fresh basil over the top. Let the loaf rest 1–2 minutes, then slice into serving pieces (about 1–1.5 inch slices). Serve warm.