These simple oven-roasted onions are tender, mellow, caramelized, and require no peeling! Baked as halves, whole, or quartered to serve as a versatile side and on your holiday table!

I love to have multiple roasted vegetable side dishes to hand that I can rely on for meal prep, special occasions, or even simple mid-week meals. I’ve already shared recipes for roasted broccoli and cauliflower and maple/honey-roasted carrots. Now it’s time to share how to roast onions!

These oven-roasted onions are tender (almost creamy) in the middle with a mild, caramelized, subtly sweet, slightly crisp top and gentle infusion of fresh thyme flavor and have become a new favorite side (though roasted garlic is still my favorite roasted ingredient ever!).

Not only is the onion side dish easy to prepare but it also stores well – you can meal-prep it for several days and keep it in the freezer for up to 12 months! Plus, the onions won’t be out of place on your holiday table either, alongside all your Thanksgiving/Christmas favorites, like creamy mashed potato, green bean casserole, brown gravy, etc.

Furthermore, I’ve included methods for how to make whole roasted onions, halved pieces, and quarters, depending on what works best for your dish. And if you want to explore other methods of enjoying onions, check out my recipes for caramelized onions, pickled onions, crispy fried onions, and even onion powder!

The Ingredients

This roasted onion recipe requires just a handful of ingredients with plenty of options for versatility. I’ve used:

• Onions: I used unpeeled medium yellow onions. However, this method should also work with red onions or white onions.  
• Oil: I used extra virgin olive oil, though any neutral cooking oil will work.
• Sea salt: added to taste. You can also add black pepper if desired.
• Lemon thyme: to help infuse the baked onions with extra flavor.

Optional Add-ins and Variations

• Balsamic vinegar: drizzle a tablespoon over the onions before baking for delicious balsamic onions. It also pairs wonderfully with the thyme roasted onions.
• Sumac: a sprinkle of sumac tastes wonderful with the onions.
• Other herbs: rosemary is another favorite of mine, and perhaps oregano or sage (or a combination of several, finely chopped) would work great too.
• Butter: alongside the oil, add some melted butter for extra richness or make whole roasted onions, each with a tiny pat of butter.
• Garlic: sprinkle them with a bit of garlic powder for extra flavor. Alternatively, gently press fresh garlic into each onion half to infuse the flavor throughout.
• Other vegetables: there are several veggies you could combine with this baked onion recipe, including roasted potatoes, peppers, etc.
• Parmesan cheese: serving the baked onions with cheese may sound odd but is actually delicious.
• Sweetener: to enhance the natural sweetness from the roasted onions, you can add a small drizzle of a liquid sweetener – honey, agave, maple syrup, etc. Alternatively, you could sprinkle them with brown sugar in the last 10-15 minutes of baking.

How to Roast Onions? (Halved)

First, preheat the oven to 350ºF/180ºC.

Then, slice the onions in half. There’s no need to peel them (unless you prefer to at this point).

Next, place the fresh thyme into a large oven-safe dish or rimmed baking sheet (by placing it UNDER the onions, it won’t burn in the process). Then drizzle olive oil over it.

Next, spread the onion halves, cut-side down, and sprinkle the entire dish with a bit of salt.

Then roast in the oven for 40-45 minutes, until the onions are tender and wonderfully caramelized/golden brown.

The exact baking time will vary based on the size of the onions you’re using, so keep an eye on them. You can check if they’re tender with the tip of a sharp knife.

Whole and Quartered Baked Onions

For quartered onions/onion “wedges”: the method is similar, but peel them first if preferred. Then roast for 30-35 minutes. Flip halfway, so both cut sides have contact with the pan and air.

Whole roasted onions: peel most of the layers of papery skin from the onions except the final one. Cut off the very end of the root end (so they can stand up in the parchment-lined baking dish) and about 1/2 inch/1 cm from the other side, then drizzle with the oil/seasonings and bake for 60-80 minutes (the time will vary based on the size of the onions). If the onions brown too quickly, you can cover the dish with foil.

How Make Ahead and Store?

Store: allow the roasted onions to cool, peel them, transfer any leftovers to an airtight container/bag, and store them in the refrigerator for 3-5 days.

Freeze: when properly stored, cooked onions can last almost indefinitely in the freezer. However, I recommend using them within 10-12 months. Start by flash freezing them until solid, then transfer them to a freezer-safe container/Ziplock style bag (squeezing out excess air).

Allow them to thaw in the refrigerator overnight before enjoying/reheating. They’ll last an additional 2-3 days after thawing.

Reheat: you could reheat the onions in the microwave or chop them up and reheat them on the stovetop.

Serving Recommendations

• Over grains: I find these baked onions work particularly well with grain heavy meals like quinoa, couscous, farro, etc.
• Soup: you can slice the onion and use it as a soup topper or blend it into the soup for extra flavor.
• With Protein: roasted onion pairs well with all sorts of seafood (including shrimp, scallops, white fish, etc.), chicken (like roasted chicken or chicken kabobs), beef dishes (like steak), and things like these lamb kofta – so have fun experimenting.
• With burgers: either alongside or chopped up as a burger topping.
• Frittata/quiche: chop the baked onions and mix them into a frittata/quiche for more flavor.
• Pasta: serve alongside or mix into pasta dishes including mac and cheese, baked feta tomato pasta, one-pot vegetable pasta, lasagna, etc.
• Potatoes: enjoy them alongside creamy mashed potato or mashed sweet potato, crispy smashed potatoes, etc.
• Bread: finely chop and add to bread dough for extra flavor.

These oven-roasted onions will also work well when cooled and added to salads or as part of your roast dinner, at Thanksgiving, or Christmas!

Recipe Notes and Tips

• Use similar-sized onions: that way, they’ll roast evenly.
• Roasting time varies: depending on the size of the onions and if they’re much smaller/larger than the ones I use.
• Avoid overcrowding: this will ensure the onions become wonderfully caramelized rather than just steaming from proximity.
• Be careful not to overbake: otherwise, the onion can become dry and/or burned.
• Remember to peel: I find it easiest to do so after roasting the onions. However, you can do it beforehand if preferred. Don’t attempt to eat the papery skin, though, as it won’t be pleasant.

Simple Vegetable Sides

• Roasted cherry tomatoes
• Oven-roasted garlic butter corn on the cob
• 10-minute air-fried green beans
• Crispy parmesan potato stacks
• Simple stir-fried vegetables
• Honey roasted carrots
• Lebanese Hindbeh (sauteed dandelion greens/spinach)
• How to Make Onion Jam

If you try this oven-roasted onion recipe, I’d love to hear your thoughts and/or questions below. Also, I’d appreciate a recipe card rating below, and tag me in your recipe recreations on Instagram @Alphafoodie!