Preheat the oven to 400°F (200°C). Line a large baking sheet with parchment paper.
Cut the loaf of French bread lengthwise into two halves and place both cut sides up on the prepared baking sheet.
Brush the cut sides evenly with the melted unsalted butter and sprinkle the garlic powder over both halves.
Loosely cover the bread with a piece of aluminum foil and bake for 5 minutes to warm the bread.
While the bread bakes, remove the seeds from the jalapeno peppers and chop them. Reserve 2 tablespoons of the chopped jalapenos for topping and set aside.
In a medium mixing bowl, combine the softened cream cheese, sour cream, the remaining chopped jalapenos, the salt, and the black pepper. Mix until smooth and well combined.
Remove the bread from the oven and uncover. Spread the jalapeno-cream cheese mixture evenly over both bread halves, dividing it between the two pieces.
Evenly top both halves with the shredded mozzarella and shredded cheddar cheeses.
Sprinkle the reserved 2 tablespoons of chopped jalapenos over the cheese.
Return the baking sheet to the oven and bake for 2 to 4 minutes, until the cheeses are melted.
Remove the bread from the oven and transfer to a cutting board. Let cool for a few minutes.
Slice the bread into serving pieces and serve.