Overview

Grilled cheese is elemental. All you need is the right cheese (I like Gruyere or sharp cheddar), the right bread (I go for a soft sandwich bread), a little butter and a pan, and you’re on the way to a quick, simple, satisfying meal. Or at least the main thrust of one, rounded out by good old tomato soup and/or a salad.

But you don’t need a recipe for a plain grilled cheese sandwich, do you? What you need is a recipe that takes grilled cheese to the next level with just a couple of smart additions, like the ones Raquel Pelzel offers in her terrific new book, “Umami Bomb.” She focuses on ingredients that can add umami, the delectable fifth taste that’s sometimes called savory. But not just a touch of umami. As you can tell by the title, this is about a real punch of flavor, about vegetarian recipes that, as she says in the subtitle, “explode with flavor.”

The umami-rich ingredients include aged cheeses, soy sauce, tomatoes, mushrooms, smoke, nutritional yeast and, in the case of these sandwiches, caramelized onions and miso.

I’m an avowed fan of all of the above, with such an affection for the last two on the list that I had little doubt about which recipe I’d pick from Pelzel’s book. And I wasn’t disappointed. It takes a bit of time to properly caramelize onions, of course, but after that, the recipe goes almost as quickly as a conventional grilled cheese: You just mix up the miso with butter and whole-grain mustard and slather that on the inside of the sandwiches, with plain butter on the outside for pan-frying. The result is as indulgent as you’d expect when eating grilled cheese for dinner (this is not health food by any means), but with a welcome tang and, of course, the “pow!” of umami in every bite.


Ingredients

1 tablespoon extra-virgin olive oil

1 large yellow onion (1 pound), thinly sliced

1/8 teaspoon kosher salt

1 tablespoon rice vinegar, preferably unseasoned

3 tablespoons unsalted butter, at room temperature (may substitute vegan butter, such as Earth Balance), divided

2 teaspoons white or dark miso paste

1 tablespoon whole-grain mustard

4 slices good-quality sandwich bread

4 ounces grated Gruyere cheese (1 cup; may substitute vegan shredded cheese, such as Violife or Daiya)

Cornichons (a.k.a. gherkins), for serving (optional)


Steps

Step 1

In a large skillet over medium-high heat, heat the oil until shimmering. Add the onion and salt and cook, stirring often, until the onions start to soften and brown, 5 to 6 minutes. Reduce the heat to medium-low and cook, stirring occasionally, until the onions are deeply browned and sticky, 30 to 45 minutes. Stir in the vinegar. Transfer the onions to a small bowl.

Did you make this recipe? Take a photo and tag us on Instagram with #eatvoraciously.

Step 2

In a small bowl, mix 1 tablespoon butter with the miso paste and mustard. Spread one side of each bread slice with the miso butter. Spread the other sides with the remaining 2 tablespoons butter.

Step 3

Return the skillet to medium-low heat. Place two of the bread slices, plain-buttered-side down, in the skillet. Divide the cheese and onions evenly between them and top with the other bread slices, plain-buttered-side up. (You want the miso butter on the inside of the sandwiches.) Cook until the bread is golden brown, 5 to 7 minutes. (Resist the urge to press the sandwich with a spatula.) Flip the sandwiches over and cook on the other side until the bread is golden brown and the cheese is melted, 5 to 7 minutes. Transfer to plates and serve with cornichons, if desired.

Adapted from “Umami Bomb: 75 Vegetarian Recipes That Explode With Flavor” by Raquel Pelzel (Workman, 2019).

Tested by Joe Yonan; email questions to voraciously@washpost.com.

Scale and get a printer-friendly version of the recipe here.

Did you make this recipe? Take a photo and tag us on Instagram with #eatvoraciously.

More vegetarian recipes from Voraciously:

This genius sauce turns your pasta into a seasonal stunner — no matter the season

Fried rice was made for those containers of leftover takeout in your fridge

This quick Korean stir-fry serves up a bounty of fresh-cut vegetables

Nutrition

Calories: 620; Total Fat: 45 g; Saturated Fat: 24 g; Cholesterol: 105 mg; Sodium: 960 mg; Carbohydrates: 33 g; Dietary Fiber: 2 g; Sugars: 7 g; Protein: 22 g.