How do I get mixed vegetables to finish cooking at the same time?

The one-tray roast is a good idea that produces burnt courgettes and raw parsnips as often as it produces dinner. There is no trick to it beyond accepting that different vegetables need different times, and then deciding whether to solve that with the clock or with the knife.

Step by step

1. Know roughly where each vegetable sits.At 200–220°C in pieces of a similar size: whole small potatoes, celeriac, swede, beetroot and large parsnip pieces, 40–50 minutes. Potato chunks, carrot, squash, sweet potato, 30–40. Onion wedges, fennel, aubergine, whole garlic cloves, 25–30. Cauliflower and broccoli florets, 20. Courgette, peppers, mushrooms, 15–20. Cherry tomatoes, asparagus, green beans, spring onions, 10.
2. Choose the staggered method when you want each vegetable at its best.Start the slowest group, set a timer, and add each subsequent group as its time comes up. Toss everything together when the last group goes in. It means going back to the oven two or three times and it gives the best result.
3. Choose the cut-to-suit method when you want to walk away.Everything goes in at once, but the slow vegetables are cut small and the fast ones are cut large or left whole. Parsnip in 2 cm dice and courgette in 4 cm chunks will finish together. This is the practical answer most weeknights.
4. Give everything space and enough fat.A single layer with gaps, across two trays if necessary, and enough oil to coat everything properly. A crowded tray steams, and steamed vegetables all go soft at the same rate, which solves the timing problem in the worst possible way.
5. Put the slow things where the oven is hottest.Most domestic ovens have a hot spot, usually towards the back or the top. Put the densest vegetables there and rotate the tray halfway through.
6. For the hob, use the same logic in a pan.Onion and carrot first, then peppers and courgette, then anything green, then herbs and garlic at the very end. A stir fry is the extreme version of this and the order is the whole technique.
7. For boiling, use one pan and a timer rather than several pans.Add each vegetable at its own time to the same pan of boiling salted water — potatoes first, carrots a few minutes later, greens for the last three minutes. One pan, one drain, and only the timings to keep track of.

Tips

• Par-boiling the dense roots for ten minutes before they hit the tray brings them down into the same band as everything else and gives a better texture too.
• Whole garlic cloves in their skins, halved lemons and sprigs of rosemary or thyme all survive a full roast and season everything around them.
• Anything with a lot of sugar — beetroot, red onion, tomatoes, sweet potato — catches faster than it cooks. Put those on the cooler part of the tray or add them later.
• Frozen vegetables go in from frozen at the end. They are already blanched and only need heating and browning.

Common mistakes

• Cutting everything to the same size regardless of vegetable — Size is your main tool for equalising times. Uniform cutting only works if you are also staggering the tray.
• Piling everything onto one tray to save washing up — A crowded tray steams, and then nothing browns and everything finishes soft. Two trays is not optional at volume.
• Adding delicate vegetables at the start 'because they will be fine' — Courgette and tomatoes given 45 minutes are not fine. They collapse and release water over everything else.

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