Place the sweet potato, butternut squash and cauliflower together in a steamer and steam for 10-15 minutes until soft.
Bring a large pan of boiling water to the boil, add 200g macaroni and cook for 10 minutes or so, until just soft. I don't usually salt the water when I'm cooking for the kids but feel free to if you want.
Pre-heat the oven to 180°C (fan)/200°C/gas mark 6. Melt 25g butter in a small saucepan. Stir through 1 tbsp flour and whisk in 500ml milk. Bring to the boil, then reduce the heat and cook, stirring often, for around five minutes. Don't worry about the sauce thickening too much as you want it to be on the runny side for macaroni cheese.
Remove from the heat and add 100g grated cheddar cheese. Stir until melted.
Add the cooked vegetables to the sauce and blend until smooth. Season to taste with salt and pepper if desired.
Add the cooked pasta and mix well. If you like you can serve it like this or if you prefer then transfer to an ovenproof dish, sprinkle over 50g breadcrumbs and grate a little more cheese over the top. Cook in the pre-heated oven for 20 minutes or until bubbling and the top is golden.