This Sweet Onion Casserole with Crispy Topping is a unique make ahead side dish. Onion is so overlooked as a vegetable, often it just added to dishes rather than being the star of the dish. This easy Thanksgiving side takes onions and turns them into the BEST kind of dish. One that is packed wth flavor and goes with everything!
Everyone always has onions in the pantry or refrigerator, yet they are so often relegated to being chopped and added to other dishes. I do it myself, so many mid-week meals start with a chopped onion. And for good reason, onions add so much flavor to dishes.
So why not use that flavor and make it the shining star in a dish. And that is exactly what this Sweet Onion Casserole does. It takes thinly sliced onions and cooks them slowly in butter (or olive oil for vegans) and turns them into a melting sweet mass of deliciousness.
Top that with some crispy breadcrumbs and the dish is complete. Perfect for serving with roast turkey, roast beef, glazed ham or something rich like duck or goose.
So you know that means this Sweet Onion Casserole with Crispy Topping is just PERFECT for the holidays!
Go on pin it now and make it this Thanksgiving!
How to make Onion casserole
Onion casserole is sweet onions slices cooked slowly in butter until meltingly tender and then topped with a delicious crispy topping.
You will need to slice the onions thinly for this dish. This is what creates the magic. The onions melt and meld together to make an almost creamy dish without any cream!
The quickest and easiest way to do this is to use a slicer attachment on your food processor. You can also use a mandolin but please for the love of sam use the finger guard! Those blades are lethal! Obviously you can go old school and use a sharp knife. It is possible, but far more time consuming.
What do you make the crispy topping out of?
Many people use ritz crackers for the topping, but I find they can overpower the sweet flavor of the onions. Instead breadcrumbs are fried in olive oil, until crisp and then added to the casserole. This adds a great crunch but still allows the meltingly tender onions to shine.
And that is the point of this dish, to celebrate the sweet onion!
Which onions to use for onion casserole?
All onions are not created equal, so the onion you pick can really make a difference to the dish.
I know this is a sweet onion casserole, but you don’t want to use a sweet onion like Vidalias. They don’t have enough flavor. The best onions for this dish are you basic yellow onions or brown onions. They have great flavor and get nice and sweet when cooked slowly, they also hold their shape well so your casserole doesn’t end up as onion mush. Plus they have the added bonus of being the cheapest onion. And with the cost of holiday food always good to have a delicious budget friendly side!
Can I make this Onion Casserole ahead of time?
You sure can!
Like so many of my holiday sides, these can be made ahead and then just reheated whilst the meat is resting.
You can either heat these in the oven or just heat in the microwave and then finish in the oven.
To make ahead, cook the onions as directed. Then once you have transferred them to the casserole dish, cover tightly and refrigerate for up to 24 hours.
The breadcrumbs can be crisped up to a week in advance and then just kept in an airtight jar or ziplock bag.
Then come your big day you just assemble the casserole and bake for 30 minutes until hot and bubbly! Or heat the onions in the microwave, then top with the breadcrumbs and finish in the oven for 5 minutes.
Why not pin this recipe for Sweet Onion Casserole with Crispy Topping Pin it here.
Sweet Onion Casserole with Crispy Topping
- 2.5 lb onions
- 1 stick butter
- 1/2 tsp salt
- 3/4 cup water
- 2 tsp sugar
- 2 tsp balsamic vinegar
- 1 cup panko breadcrumbs
- 1 tbsp olive oil
- 1 tsp chopped chives
- 1 tsp chopped parsley
- If cooking and serving immediately pre-heat the oven to 350ºF/175ºC
- Peel and finely slice the onions. (see note 1)
- Heat the butter in a large dutch oven or high sided skillet.
- When it has just melted add in the onions and salt then stir to coat everything in the butter.
- Cook, uncovered over a low heat for 30 minutes until the onions are soft but not coloured.
- Turn up the heat and add the water, sugar and balsamic vinegar.
- Let the mixture bubble gently for 10-15 minutes until the liquid has evaporated and the onions are melting tender.
- Transfer the onions to a casserole dish and either continue to the next step or keep refrigerated for up to 24 hours. (see below for more prepare ahead instructions)
- heat the olive oil in a non-stick skillet and add in the breadcrumbs, cook over a medium heat until the breadcrumbs start to color. Remove the pan from the heat and immediately tip the crumbs into a cold bowl. This stops the breadcrumbs from burning.
- Sprinkle the breadcrumbs over the hot onions and cook for 10 minutes to allow everything to meld together.
- Sprinkle over the fresh herbs and serve.
To prepare ahead.
- Cook the onions up to the stage where you place them in the casserole. Then cover tightly and refrigerate for up to 24 hours.
- Prepare the breadcrumbs and store in an airtight container or ziplock bag for up to 5 days.
- Place the onions in the oven and cook for 20 minutes until hot, sprinkle over the breadcrumbs and cook for a further 10 minutes.
- Alternatively reheat the inions in the microwave (around 7 minutes) and then cover with the breadcrumbs and bake for 10 minutes.
- Sprinkle over the fresh herbs and serve.
- The quickest and easiest way to slice the onions is to use a slicer attachment on your food processor. You can also use a mandolin but please for the love of sam use the finger guard! Those blades are lethal! Obviously you can go old school and use a sharp knife. It is possible, but far more time consuming.
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