Preheat the oven to 180º C. Start with the cheese sauce. Melt the butter in a saucepan. Add the flour and whisk into the foaming butter until combined. The roux will be quite firm at this point. Add the milk in stages, whisking all the while. Once the milk is absorbed, repeat the process several times until you have used all the milk. This method ensures a lump-free consistency and eliminates a ‘raw’ flour taste. Stir through the Dijon mustard and season with salt. Add the cheese to the white sauce and stir until melted.Spread the cauliflower florets onto a roasting tray, drizzle with olive oil and season. Toss to coat and roast for about 20 minutes.For the crumb topping, mix all the ingredients together in a bowl. Rub through by hand to ensure the breadcrumbs are well coated.Turn the oven up to 200º C. To assemble the Mac and Cheese, pour the cheese sauce over the cooked macaroni. Add the cauliflower and fold through. Transfer to a baking sheet and spread the parmesan crumbs on top. Don’t press down as you want the crumble to be light and chunky. Bake for about 15 minutes until golden and eat.Recipe reprinted with permission of Bibby's Kitchen@36. To see more recipes, please click here.To receive quick and convenient weekday recipes, join our Easy Weekday Meals mailing list, and for up-to-date trending food, restaurant and wine news subscribe to our Editor’s Weekly newsletter.