Preheat the oven to 400°F (200°C). Using a sharp serrated knife, slice the loaf crosswise into 8 equal thick pieces (about 1 to 1.5 inches each). Set the pieces on a baking sheet, cut-side up, spaced slightly apart so cheese can melt without overflowing too much.

Assemble cheese topping

Combine the shredded mozzarella and grated Parmesan in a bowl and toss briefly to mix. Reserve until ready to top the bread slices.

Garlic Butter

Make garlic butter

In a small bowl, mash the softened butter with a fork until smooth. Stir in the minced garlic, olive oil, chopped parsley, salt, black pepper, and red pepper flakes (if using) until evenly distributed. Taste and adjust salt or garlic to preference.

Butter the bread

Spread about 1 tablespoon of the garlic butter mixture evenly onto the cut surface of each bread piece, covering edge to edge so every bite is flavored.

Assembly & Baking

Top and bake

Divide the cheese mixture evenly among the 8 buttered bread pieces, pressing the cheese lightly so it adheres to the buttered surface. Place the baking sheet in the preheated oven and bake for 8–10 minutes, until the cheese is melted and beginning to bubble.

Broil for color (optional)

If you prefer a golden browned top, switch the oven to broil on high and broil the garlic breads for an additional 1–2 minutes, watching closely to prevent burning. Remove when cheese is golden and edges are crisp.

Finish and serve

Let the pieces cool on the baking sheet for 1–2 minutes, then transfer to a serving plate. Optionally sprinkle a little extra chopped parsley and a light dusting of Parmesan. Serve warm.