To roast vegetables in the oven, place oil-tossed vegetables on a roasting pan in the stove after it has been preheated to 450 degrees Fahrenheit, then cook them for about 30 minutes. Using a high temperature helps to caramelize the outside of the vegetables while retaining their flavor.
The most ideal vegetables for roasting include potatoes, onions, carrots and other root vegetables. While green beans and broccoli are also fine for roasting, they tend to shrivel somewhat in the extreme heat. For extra flavor, add several cloves of garlic, fresh rosemary, sage, oregano and a few sprigs of thyme to the vegetables before roasting. When fresh herbs are not available, dried versions of the same herbs still lend some flavor.
Roast the vegetables uncovered for about 30 minutes, and then remove smaller vegetables that cook faster. Toss the remaining vegetables and return them to the oven for another 10 to 15 minutes until the vegetables are brown around the edges. The timing depends on the sizes and types of vegetables you choose to combine. It is best to cut large vegetables, such as potatoes and many onions, into small pieces to allow them to cook thoroughly. Cauliflower cooks best when broken into florets, while leeks cook evenly when cut in half length-wise.