3 tablespoons butter
4 tablespoons extra-virgin olive oil, divided
4 cloves garlic, finely minced
pinch red pepper flakes
1/2 teaspoon dried oregano
1/4 cup minced fresh parsley or basil leaves, or a mix
Kosher salt
1 large loaf French or Italian bread (see note above), about 18 inches long and 4 inches wide, split half lengthwise and crosswise
1 (14.5 ounce) can crushed tomatoes
8 ounces freshly grated whole milk mozzarella cheese
2 ounces grated Parmigiano-reggiano