Oven Roasted Onions offer a delightful and hassle-free vegan side dish that’s bursting with flavor and simplicity. Crafted by culinary enthusiast Kathleen Higashiyama, this recipe transforms sweet onions into caramelized perfection through a roasting process enhanced by olive oil, salt, pepper, and an aromatic blend of thyme and rosemary. The preparation is a breeze, with a mere five minutes of hands-on time and 40 minutes of roasting in the oven.

The method begins by slicing medium sweet onions in half, removing outer layers, and arranging them cut-side up on a parchment paper-lined baking sheet. A generous drizzle of olive oil, along with a sprinkling of salt, pepper, and a selection of herbs, sets the stage for the magic to unfold. The onions roast at 400°F for 35-45 minutes, turning halfway through, until they achieve a tender and golden brown perfection. A simple test with a paring knife confirms their readiness, as it effortlessly pierces through the layers.

The final touch involves transferring the roasted onions to a serving dish, where they are seasoned once more with salt, pepper, and additional herbs if desired. This dish not only satisfies the taste buds but also offers practical tips, like cutting large onions into quarters for more manageable cooking and ensuring even coverage of olive oil between the layers. With a nutrition profile delivering a mere 42 calories per serving and a mere 3 grams of carbohydrates, these Oven Roasted Onions make for a guilt-free and immensely enjoyable addition to any meal. Whether accompanying a hearty main course or standing alone, these caramelized wonders are an instant crowd-pleaser, showcasing the beauty of simplicity and the power of well-balanced flavors.

Oven Roasted Onions

Oven Roasted Onions are a no-fuss vegan side that’s flavor-packed and easy to make. Caramelized sweet onions are roasted in olive oil, salt and pepper, thyme, and rosemary until tender.

Prep Time5minutes mins

Cook Time40minutes mins

Total Time45minutes mins

Course: Side Dish, Sides

Cuisine: American

Diet: Vegan, Vegetarian

Servings: 8

Calories: 42kcal

Author: Kathleen Higashiyama


  • 1 knife
  • 1 cutting board
  • 1 sheet pan
  • 1 parchment paper
  • 1 Measuring spoons


  • 2 medium sweet onions cut in half at the root
  • 2 tablespoon olive oil plus more if necessary
  • kosher or sea salt
  • freshly ground black pepper
  • fresh or dried herbs rosemary, sage, thyme, a blend


  • Prepare onion – Heat the oven to 400°F. Use a sharp knife to cut the onion in half at the root. Remove the dry outer layers of onion paper and cut off the tip of the onions. Place the onions on a parchment paper-lined baking sheet cut-side up. Generously drizzle the onions with olive oil and season with salt, freshly ground black pepper, and dried fresh herbs, like rosemary, thyme, sage, parsley, or a blend of choice.2 medium sweet onions,2 tablespoon olive oil,kosher or sea salt,freshly ground black pepper,fresh or dried herbs
  • Roast onions – Bake the onions on the middle rack for 35-45 minutes, or until tender and golden brown, turning over halfway. To test doneness, use a paring knife to pierce into a few layers of the onion through the side. If it goes in easily, the onions are done.
  • Serve – Transfer the roasted onions to a serving dish and season with more salt, freshly ground black pepper, and herbs, if desired. Enjoy immediately.


Top Tips

  • Cut large onions into quarters so they are easier to cook.
  • Use similar sized onions and don’t overcrowd the pan so the onions cook evenly.
  • Get the olive oil between the onion layers so the layers cook evenly.
  • Figure out what main course you want to make ahead of time so you can make it while the onions roast.
  • Use sweet onions, such as Walla Walla, Texas Sweets, Maui, and Vidalia.
  • If you opt for a medium yellow onion, cook the onion a little longer, as yellow onions have a lower water content than sweet onions and take longer to cook.


Calories: 42kcal | Carbohydrates: 3g | Protein: 0.3g | Fat: 4g | Saturated Fat: 0.5g | Polyunsaturated Fat: 0.4g | Monounsaturated Fat: 3g | Sodium: 1mg | Potassium: 40mg | Fiber: 0.5g | Sugar: 1g | Vitamin A: 1IU | Vitamin C: 2mg | Calcium: 6mg | Iron: 0.1mg