Spread softened butter evenly on the outer sides of all 4 slices of sourdough. This will crisp and brown the exterior when grilling. On the inner side of two slices, brush about 1/2 tablespoon olive oil each (this helps prevent sogginess from the sauce).

Assemble cheese layer

On the two slices that will be the bottom of each sandwich, divide the shredded mozzarella and provolone evenly (about 1 cup mozzarella + 1/3 cup provolone per sandwich). Spread the cheese in an even layer leaving a 1/4" border to avoid overflow.

Pizza Sauce & Toppings

Add sauce

Spoon 1.5 tablespoons of pizza sauce onto the cheese layer of each sandwich (total 3 tablespoons). Spread gently to an even layer but keep away from the bread edges.

Top with toppings

Divide the pepperoni (6 slices per sandwich), black olives, red onion, roasted red pepper strips (if using), and torn basil evenly over the sauce and cheese layers. Sprinkle the dried oregano and red pepper flakes over each assembled sandwich. Season lightly with the salt and freshly ground black pepper.

Cook & Finish

Close sandwiches

Place the remaining two slices of bread (butter side out) atop each assembled bottom slice, pressing gently to compact the filling.

Cook in skillet or panini press

Option A — Skillet: Heat a large nonstick or cast-iron skillet over medium-low to medium heat. Place sandwiches buttered-side down in the skillet. Cook for 4–5 minutes per side, pressing gently with a spatula, until the bread is golden brown and the cheese is melted. If the exterior is browning too fast before the cheese melts, lower the heat and cover the pan with a lid for 2–3 minutes to help the cheese melt through. Option B — Panini press: Preheat the press to medium. Lightly brush the top of the sandwiches with the remaining olive oil. Grill for 3–5 minutes until golden and the cheese is melted.

Rest and slice

Transfer sandwiches to a cutting board and let rest 1–2 minutes (this helps the filling set so it won’t run out). Slice each sandwich in half on the diagonal. If desired, sprinkle a pinch more dried oregano or a few torn basil leaves on top before serving.