Preheat the oven to 350 degrees F.
In a bowl, mix together cream cheese, butter, mayonnaise, garlic, drained spinach, chopped artichoke hearts, both shredded cheeses, and black pepper until well combined.
Cut the French bread in half lengthwise.
Spread the spinach and artichoke filling generously on each half.
Place the loaded bread on a foil-lined baking sheet (easy clean-up!) or a greased baking sheet.
Bake for 20-25 minutes or until the bread is golden brown and the cheese is beautifully bubbly.