Preheat the oven to 425 degrees F. Place the chopped cauliflower on a baking sheet. Toss it with the olive oil, salt and pepper. Sprinkle with the garlic powder. Roast for 20 to 25 minutes, until golden and slightly charred.

Reduce the oven heat to 375 degrees F. Bring a salted pot of water to a boil.

Heat a pot over medium-low heat and add butter. Once sizzling, whisk in the flour and cook until fragrant and golden in color. Slowly whisk in the milk. Cook until the mixture thickens, about 5 to 6 minutes. Reduce the heat to low and stir in the cheeses, one small handful at a time, until melted. Stir in the mustard, nutmeg and a pinch of salt and pepper.

Cook the pasta according to its directions. Once the pasta is cooked, stir it and the cauliflower into the cheese sauce.

Pour the pasta in a dish and top with the breadcrumbs. Bake for 30 to 35 minutes, until golden and bubbly. Top with fresh herbs before serving.