This Sweet Onion Casserole with Crispy Breadcrumbs 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 dish takes onions and turns them into the BEST kind of casserole - one that is packed wth flavor and goes with everything!
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.
To re-heat.
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.
Notes
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.