Choosing The Right Onion Can Completely Change Your Casserole

When putting together a casserole, aromatics like onions tend to get relegated to an afterthought. Whether red, yellow, or white, you might just toss in whatever you have on hand, yet in some recipes, the type of onions can genuinely make or break the final result. Take it from Tara Bench, the cookbook author and blogger behind Tara Teaspoon, who gave Tasting Table exclusive advice about how to choose and use onions for the best casseroles,

"It really depends on the casserole style and flavor profile of the recipe!" Bench says. "Sweet onions like Vidalia and Walla Walla offer an obvious mild, sweet flavor profile, caramelize beautifully, and cook to a softer texture," she explained, adding that they are "traditional in Southern-style casseroles." For instance, in a show-stopping Tennessee onion casserole, sweet onions offer the best sugary-savory, caramelized profile, without making such an onion-centric dish too assertive.

"Yellow or Spanish onions ... are firm and hold their shape and bite, while giving the dish a deeper savory flavor," Bench says, calling them "super versatile." This is also a key texture difference between white and yellow onions. If you don't want the allium to completely dissolve into your casserole, standard yellow is the way to go. 

Both sweet and yellow onions are great casserole choices, but if you want to highlight their uniqueness, Bench suggests some complementary ingredients. "Sweet onions cook into jammy goodness, and their slightly sweet flavor pairs well with nutty Gruyère cheese and thyme or rosemary," she says. "I think about French onion soup flavors, or a salty and nutty parmesan." Sweet onions are a must-use for dishes like cheesy French onion soup pasta casserole, and would also go well with other salty Italian cheeses like Pecorino Romano and Grana Padano. "In a casserole I'd pair them with butter and cream, potatoes, mushrooms and toasted breadcrumbs," Bench added. Try adding jammy sweet onions, sauteed mushrooms, and a crunchy crumb crust to potatoes au gratin with Gruyère to taste the magic.

As for yellow onions, Bench prefers "potent flavors like bacon and sharp cheddar that can stand up to the stronger onion. Also a classic chicken, rice, and green bean combo, where I don't want a sugary sweet onion competing with more mild ingredients." Use yellow onions in recipes like savory breakfast bagel casserole with bacon, cheese, and eggs, as the sturdy allium won't get lost in the mix of bold elements. An overt caramelized onion sweetness may also taste out of place in dishes that are meant to be lighter, like a chicken, lemon, and rice casserole or seafood casserole. For these dishes, opt for the more savory yet versatile yellow onion.