Breakfast casseroles are delicious, but too few offer vegetarian options that are hearty enough to stand up to the bacon and sausage-laden classic breakfast dishes. Vegetarian breakfast casseroles often go extra-light, with fresh green vegetables or a smattering of herbs in the eggs. Well, not this one. This is a hearty vegetarian breakfast casserole with all the rich, deep flavor you'd usually get from meat, but even better.

The flavor boost in this easy dish comes from two things: hot mustard and sun-dried tomatoes. Spicy mustard adds a piquant flavor -- not easily identifiable, but a strong supporting player in the background. (Don't worry -- this doesn't taste overwhelmingly of mustard!)

Then there are sun-dried tomatoes, preferably really good ones packed in oil (perhaps with some herbs) to give umami flavor and a little bit of meaty chew here and there. The cheddar adds great flavor to the mix, too. If you're feeling fancy, throw in a few leaves of rosemary or thyme, but it doesn't need it.

This dish is truly hearty; it's packed with more potatoes than I usually put in a casserole of this size. But the texture is still light and even fluffy, thanks to the shredded potatoes, which don't weigh this down like cubed potatoes can.

It's a great make-ahead breakfast. Make a pan of this and serve for brunch -- or just to take a wedge with you to the office every morning for a few days.

Cheesy Potato Breakfast Casserole with Cheddar and Sun-Dried Tomatoes

8 to 10 servings

1 tablespoon unsalted butter

1 small onion, diced

6 cloves garlic, minced

2/3 cup sun-dried tomatoes, preferably oil-packed, sliced into thin strips

9 large eggs

3 tablespoons hot mustard

1 cup whole milk

1 1/2 teaspoons salt

1/4 teaspoon freshly cracked black pepper

2 cups shredded Cheddar cheese

6 cups (or 1 pound) shredded frozen potatoes

Lightly grease a 9- by 13-inch baking dish with nonstick spray or olive oil. In a large skillet, heat the butter over medium heat until it melts and foams up. Add the onion and garlic and cook for 5 minutes, or until the onion has softened. Add the sun-dried tomatoes and cook for about 5 minutes or they are fragrant and the onion is nearly translucent and beginning to brown around the edges. Turn off the heat.

In a separate bowl, beat the eggs thoroughly with the mustard. Whisk in the milk. Stir in the salt and black pepper. Fold in the Cheddar cheese, frozen potatoes and vegetables from the skillet. Transfer the mixture to the baking dish. (At this point the casserole can be baked immediately or covered and refrigerated for up to 24 hours.)

Bake at 350 F for 35 to 45 minutes, or until the eggs are firm and the top is slightly golden. Serve immediately with a fresh salad or fruit.

(Faith Durand is managing editor of TheKitchn.com, a nationally known blog for people who love food and home cooking. Submit any comments or questions to kitchn@apartmenttherapy.com.)