Roasted onions are wonderfully flavorful and caramelized. They make a wonderful side dish or topping for many different meat and poultry dishes.
Even if you're not a fan of them in their raw state (I'm not), I think you will love them oven-baked. They are mellow and sweet.
Raw onions are quite sharp. I tend to avoid them. But something magical happens when you cook them. They become creamy and mild, almost sweet.
Baking onions in the oven makes them tender, browned, and very flavorful. This is a recipe that I like to make because it's truly easy, yet it produces delicious results.
It's also a very versatile recipe - you can use the roasted onions as a topping or even as a side dish all on its own.
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Ingredients
You'll only need three simple ingredients to make this tasty side dish. The exact measurements are included in the recipe card below. Here's an overview of what you'll need:
- Medium onions: White or yellow onions work well in this recipe (here's the difference between different onion colors), although I usually tend to use yellow ones.
- Butter: I use plenty of butter - 2 tablespoons per medium onion plus more for the pan. The butter adds wonderful flavor to the dish. Another tasty option would be to use olive oil. But personally, I prefer butter.
- Kosher salt: I use kosher salt in most of my recipes, this one included. If using fine salt (such as sea salt), you should use half of the amount listed, or the dish could end up too salty.
Variations
Since the onions themselves are so flavorful, I don't usually add any other seasonings. But if you'd like, you can season them with garlic powder and oregano.
You can also sprinkle them with grated parmesan cheese after the first 20 minutes of cooking.
Roasted Onions Instructions
Scroll down to the recipe card for the full details. Here are the basic steps for making this recipe:
- Your first step is to peel the onions, slice off their edges, then cut them into four or five thick slices, as shown in the video below.
- Now, place the slices in a well-buttered rimmed baking dish. Coat them with melted butter and sprinkle them with Kosher salt. (Photo 1).
- The last step is to bake the onions until golden brown. This should take about 40 minutes in a 400°F oven. (Photo 2).
- You should flip the slices midway through baking. (Photo 3).
Expert Tip
Keep a close eye on the onions during the last 10 minutes of baking to ensure they don't burn. Your oven might run hotter than mine.
Recipe FAQs
We don't often think about onions as a separate side dish. We tend to use them as an ingredient in other recipes. But in this case, they do make a wonderful, very flavorful side dish.
Onions contain a relatively large amount of sugar. During the cooking process, large sugar molecules are broken down into smaller ones and those have a sweet taste.
White onions are sweeter and milder than yellow ones. They're not as pungent when served raw.
I wouldn't use yellow onions in a recipe that calls for raw white ones. But if a recipe calls for cooking yellow onions, it's fine to use white onions instead.
Serving Suggestions
This lovely side dish goes really well with meat and poultry dishes. Since I bake it in a 400°F oven, I like to serve it with a main dish that I can cook in the same oven. It's just so convenient!
So, among other choices, I often serve roasted onions with baked pork chops, baked meatballs, or beef tenderloin roast.
They also make a wonderful topping for hamburgers and steaks, including broiled hamburgers, turkey burgers, bison burgers, Tri-tip roast, New York strip steak, and ribeye steak.
Storing Leftovers
The leftovers keep quite well in the fridge, in a sealed container, for 3-4 days. Reheat them, covered, in the microwave at 50% power.
The leftovers are also very good when chopped and mixed into an omelet or a scramble, such as spinach and eggs scramble, fluffy scrambled eggs, and egg white omelet.
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Recipe Card
Roasted Onions Recipe
Ingredients
- 2 tablespoons butter plus more for the pan
- 1 medium onion
- ½ teaspoon Diamond Crystal kosher salt
Instructions
- Preheat your oven to 400°F.
- Grease a square 8-inch Pyrex baking dish with butter.
- Peel the onion and slice it into ¼-inch-thick slices, as shown in the video below. You will probably end up with five slices.
- Arrange the slices in a single layer in the prepared baking dish. Melt the butter and pour it all over the onions. Sprinkle with Kosher salt.
- Roast the onions until the bottoms are golden, about 20 minutes.
- Turn the onion slices to the other side and bake them until golden-brown, about 20 more minutes.
Video
Notes
Add Your Own Notes
Nutrition per Serving
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Vered DeLeeuw, LL.M., CNC, has been following a low-carb real-food diet and blogging about it since 2011. She's a Certified Nutrition Coach (NASM-CNC), has taken courses at the Harvard School of Public Health, and has earned a Nutrition and Healthy Living Certificate from Cornell University. Her work has appeared in several major media outlets, including Healthline, HuffPost, Today, Women's Health, Shape, and Country Living. 
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