Different vegetables will roast faster than others. Root vegetables are great slow roasters while asparagus will be done very quickly. Broccoli and cauliflower fall somewhere in the middle
One way to deal with this is to use a separate tray for the quicker roasting vegetables. You can put them in the oven a bit later and take everything out at the same time.
2 medium carrots
2 medium parsnips
1 medium sweet potato
half a head of cauliflower
small bunch of broccoli
Preheat your oven to 425 C.
Cut vegetables into pieces all roughly the same size (about 1 inch around) so that they cook evenly. Make a separate pile for the carrots, parsnips and sweet potato, and another for the broccoli and cauliflower.
In a medium bowl toss each batch in olive oil until well coated. Season with sea salt and pepper.
Lay each batch out on its own baking tray, which has been covered in parchment paper. Do not crowd the vegetables or they will not crisp nicely.
Place the root vegetables in the oven for 30 minutes.
Place in the cauliflower and broccoli tray in the oven about 15 minutes after the root vegetables.
Give the trays a good shake to turn the vegetables at least once during roasting.
Remove when the vegetables are golden on the outside and tender inside.