Preheat oven to 350℉. Slice loaf of bread in half lengthwise, cutting each half into equal thickness if possible. Set aside.
1 loaf French bread
In a medium bowl, mix butter and mayonnaise until smooth. If butter is not fully softened, it's fine, just mix as well as possible. Add Parmesan, garlic, and scallions, stirring until incorporated.
1 cup salted butter, 6 tbsp Parmesan cheese, 6 tbsp mayonnaise, 2 cloves garlic, 3 scallions
Spread mixture equally over both halves of bread. Sprinkle paprika on top to your liking. Make two boats of aluminum foil (see notes) around the bread halves. Place on the baking sheet and tent the top with aluminum foil.
paprika
Bake in the preheated oven for about 10 minutes. Remove aluminum foil from top of bread and turn oven to Broil function. Broil until the topping is well softened, slightly bubbly, and the edges of bread are golden brown. This takes 2-4 minutes depending on your oven. Watch it carefully to ensure the topping and bread don't burn. Use the edge of the bread as your guide since the topping doesn't need to change color much.
Remove bread from the oven and sprinkle with chopped parsley. Place bread on a cutting board and slice as desired. Plate and serve.