Start by taking a mixing bowl and adding the softened cream cheese. Using a hand mixer or a spatula, beat it until it’s smooth. Then, add in the mayonnaise, garlic powder, black pepper, and seasoned salt. Mix well until everything is combined. Finally, fold in both the shredded cheddar and mozzarella cheeses, creating a thick and creamy filling that’s just waiting to make your French bread sing.

Take slices of your French bread and spread a generous amount of butter on one side of each slice. On the other side, generously scoop out the cheese mixture. Make sure to spread it evenly, leaving some space at the edges to avoid overflow during cooking. Top with another slice of bread, butter side facing out, creating a delightful sandwich that will crisp up beautifully.

Place a skillet over medium heat and let it warm up for a minute or so. Once heated, add your assembled grilled cheese sandwiches straight into the pan. Cook them for about 3-4 minutes on one side, or until the bread is a lovely golden brown. Then, carefully flip them with a spatula and continue cooking until the other side also turns golden brown and the cheese inside has melted. It’s alright if you get a touch of gooey cheese escaping; that's part of the charm!