Cook the potatoes: Preheat the oven to 400 degrees F.
Toss the potatoes in enough olive oil to coat in a medium bowl. Sprinkle with salt and pepper. Pour onto a sheet pan. Bake until the potatoes are golden, crispy-skinned and soft, 20 to 25 minutes. Set aside.
Meanwhile, make the cheese dip: Melt the butter in a large saucepan over medium heat. Add the onions and cook until they are soft and translucent, then add the garlic and cook for 1 minute more. Whisk in the mustard powder, paprika, cayenne and 1 teaspoon salt; cook for an additional 2 minutes. Sprinkle the flour over the top and stir to combine. Cook for 2 to 3 minutes. Gradually whisk in the milk. Simmer, whisking occasionally, for 10 minutes.
Add the Cheddar and stir until it melts, then add the cream cheese. Once all the cheeses are melted, stir in the roasted peppers. Season with black pepper to taste and additional salt, if necessary. Keep warm on low heat or in a double boiler.
Putting it all together: Turn the boule over. Carve out the boule in large chunks, leaving a 1-inch wall. Cut the hollowed-out boule chunks into 1-inch cubes or 2-by-1/2-inch batons.
On a round platter, arrange the bread like logs or firewood, then arrange the pepper triangles on top. Set the boule in the middle. Scatter the roasted potatoes around like rocks. When ready to serve, pour the warm cheese dip into the boule. ENJOY!