I love breakfast casseroles (I wrote a whole book about casseroles and my favorite chapter was breakfast!). But I feel that 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!)
And 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 is a great flavor in the mix, too. If you're feeling fancy, throw in a few leaves of rosemary or thyme, but it doesn't need it.
This casserole 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 take a wedge with you to the office every morning for a few days.

Cheesy Potato Breakfast Casserole with Cheddar & Sun-Dried Tomatoes
8 to 10 servings
1 tablespoon unsalted butter
1 small onion, diced
2/3 cup sun-dried tomatoes, preferably oil-packed, sliced into thin strips
6 cloves garlic, minced
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 9x13-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.

More Breakfast Casseroles:
• "Ham and Cheese" Breakfast Casserole
• Apple & Cinnamon Whole Grain Breakfast Strata
• Basic Oven Omelet
• Pancetta & Cinnamon Ricotta Casserole
• Bacon, Potato & Egg Breakfast Casserole
(Images: Faith Durand)
Kart Serving Tray b...

Comments (16)
Bread puddings are another easy casserole idea that you can also portion out over the week. I sometimes put them in individual baking dishes and bake them up fresh each morning. Mushroom and Spinach Bread Pudding
Where is the mug in the background from?
@Tara, I have to be really obnoxious and say it's actually from Portugal, from my trip there last year. I've looked all over for an online source (I want to blog about them!) but haven't had any luck. They are from the Secla Vintage line, though, and we bought them at A Vida Portuguesa in Lisbon. My favorite mugs ever.
How would I go about using fresh potatoes for this casserole?
Also, I'm thinking of bringing this to a potluck breakfast at work -- how would you suggest serving it up warm to people? Should they individually nuke their own pieces? Or should I try warming up the whole dish in the microwave, or use two smaller dishes and warm them up in the toaster oven?
Not particularly nutritious. As a veg, I'd be adding some additional vegetables or at least some tofu.
I can't wait to try this!
@Indy Jeffery - Yes, because vegetarians have to eat healthily ALL THE TIME. Come on, she said right in the article that most veg breakfast options are usually light and good for you and that this was a nice rich alternative for vegetarians who really want something hot and cheesy for breakfast, but can't eat the cheesy bacon and egg bake.
@Faith, thanks anyway. Its very cute from what I can see.
Sounds yum! I know the theme is breakfast and I love it's portable nature, but I would love this for lunch or dinner too - throw a simple green salad on the side perhaps to make it really well rounded meal. Delish.
can you make this ahead & freeze it?
I made this this morning and it is definitely going in the 'make again' file! Fluffy yet comforting, just like you said. And I love that you can make it the night before. I used a strong dijon mustard because that's what I had on hand, but I'd love a recommendation for a proper hot mustard for next time. Maybe Trader Joe's Sweet & Hot? Thanks for the nice recipe!
by "hot mustard" do you mean a dry mustard like Colemans? Or just any spicy mustard?
I made this for a brunch this past weekend. While it was very tasty, it wasn't the prettiest thing to look at; it had some grayish tones to it. I wonder if that is because I used freshly grated potatoes instead of the frozen hash browns?
tweak it, and enjoy :)
Just be you..
I made this for a holiday breakfast at work last month.
I thought there was a little too much garlic so halved it. It was still very fragrant. I used some sun-dried tomatoes I found in Publix that were not oil packed but very moist - like raisins. These worked well and I thought them a particularly wonderful ingredient to include.
I baked it the night before and refrigerated it. The next morning, I warmed it in the microwave until hot again and placed it on a warmer on the buffet.
It disappeared very quickly and I had lots of compliments. Thank you