First, prepare the bread boule by slicing off the top 2 inches and hollowing out the center, leaving the walls of the boule about an inch thick. Cut the top and insides of the bread into bite-sized cubes and set aside.
In a large saucepan, melt the butter over medium heat. Add the onions and cook until soft and translucent, about 5 minutes. Add the garlic and cook for 1 minute.
Whisk in the mustard, paprika, cayenne and salt; cook for an additional 2 minutes. Sprinkle the flour over the onion/garlic mixture and stir to combine; cook about 2 minutes more. Gradually whisk in the milk and gently simmer for 2 minutes. Add the cream cheese and stir until it melts. Then add the Cheddar cheese. Once all the cheeses are melted, stir in the roasted peppers and hot green chiles. Season with black pepper to taste and additional salt, if necessary.
Preheat the broiler on high.
Scoop the pimento cheese mixture into the hollowed-out bread boule and place on a baking sheet. Broil until the top begins to bubble and lightly brown, a couple of minutes. Place the filled boule on a platter and serve immediately with the bread cubes.