This high-protein oven-baked Denver omelette casserole combines fluffy eggs, bell peppers, onions, and melted cheese in one easy breakfast bake.

It has all the classic Denver omelette flavors without standing over the stove making individual servings.

Perfect for breakfast meal prep, weekend brunch, holiday mornings, or busy weekdays, this egg casserole can be prepared ahead and reheated by the slice.

Serve it with fruit, toast, or breakfast potatoes for a filling family breakfast that keeps everyone satisfied.

If you’re into easy egg bakes and omelette-style breakfasts, these are worth bookmarking too:

Ingredients You’ll Need

Diced ham is the classic Denver choice here, but leftover holiday ham works great too if you’ve got it on hand.

I use a mix of green and red bell pepper for color and a little sweetness, and whole milk keeps the eggs custardy instead of rubbery (skim works in a pinch, just don’t expect quite the same texture).

Ingredients

12 large eggs
1/2 cup whole milk
1 1/2 cups diced cooked ham
1 cup diced green bell pepper
3/4 cup diced red bell pepper
1/2 cup diced yellow onion
2 cups shredded cheddar cheese, divided
1 tablespoon butter, for the pan and skillet
1/2 teaspoon salt
1/4 teaspoon black pepper

Directions

Preheat your oven to 375°F and set a rack in the middle position so the casserole cooks evenly.
Grease a 9×13 inch baking dish generously with the butter, working it into the corners and partway up the sides.
This casserole puffs as it bakes and the eggs cling to any bare spot in the dish, so a well-greased pan matters more than you’d think.
Skip this step and you’ll be scraping baked-on egg off the corners later, trust me.
Melt a little of the butter in a skillet over medium heat and add the diced green pepper, red pepper, and onion.
Cook, stirring occasionally, for about 5 minutes until the vegetables soften and the onion turns translucent, not brown.
You’re not looking for any color here, just softness, since raw or crunchy vegetables in a baked egg dish read as undercooked even after 35 minutes in the oven.
This step also drives off some of the water the vegetables would otherwise release into the eggs while baking.
Remove the skillet from the heat and let the vegetables cool slightly while you whisk the eggs, so you don’t accidentally scramble them.
In a large bowl, whisk the eggs, milk, salt, and pepper together until fully combined and slightly frothy on top.
Whisk for a full 30 seconds, not just a few quick strokes.
That extra bit of air is what gives the casserole its fluffy rise instead of a dense, flat texture.
A whisk with thin wires rather than thick ones incorporates air faster and makes this step even easier.
Scatter the diced ham evenly across the bottom of the greased baking dish so every square gets some in the final cut.
Add the sauteed peppers and onion on top of the ham, spreading them into an even layer.
Sprinkle half of the shredded cheddar over the vegetables, saving the rest for the top.
This ham-first order matters because it traps the vegetables between two layers of cheese, which helps everything cook evenly instead of the peppers floating up to the surface.
Pour the egg mixture slowly and evenly over everything, giving it a second to settle into the gaps before adding more.
Sprinkle the remaining cheddar over the top and slide the dish onto the middle rack of the oven.
Bake for 30 to 35 minutes, until the center is puffed and set and a knife inserted comes out clean rather than coated in wet egg.
The top should be golden in spots, not deeply browned across the whole surface (if it’s browning too fast, tent it loosely with foil for the last 10 minutes).
Every oven runs a little different, so start checking at the 28-minute mark instead of waiting for the timer.
A slight jiggle in the very center is fine when you pull it, since it keeps setting as it rests.
Let the casserole rest for 5 to 10 minutes before slicing into it.
It will deflate slightly as it cools, which is completely normal and not a sign anything went wrong.
That resting time lets the center firm up enough to hold clean slices instead of falling apart on the spatula.
Slice and serve warm straight from the dish and enjoy!

Important Recipe Notes

Use fully cooked ham. Since this bakes rather than fries, make sure your ham is already fully cooked (deli ham, a diced ham steak, or leftover holiday ham all work well here). Raw pork shouldn’t go into a casserole like this since baking alone won’t cook it through reliably.
Don’t skip the vegetable saute. Raw peppers and onion release a good amount of water as they bake, and that extra moisture can leave you with watery eggs. Softening them in a skillet first drives off some of that liquid and takes the sharp edge off the onion.
Check doneness with a knife, not just the clock. Ovens vary enough that 30 minutes in one might mean 38 in another, so don’t rely on the timer alone. Insert a knife into the center of the casserole; it should come out clean, without any wet egg clinging to the blade.
Let it rest before cutting. Cutting into the casserole straight out of the oven means the slices fall apart on the way to the plate. Give it 5 to 10 minutes to firm up first, and you’ll get clean squares instead of a scramble.

Give yourself a little extra prep time. Dicing the ham, peppers, and onion adds a few extra minutes up front, more than you’d spend on a basic scrambled egg breakfast. It’s worth the tradeoff for a dish that feeds six without you standing at the stove the whole morning.
This one is easy to make ahead. You can assemble the whole casserole the night before, cover it tightly, and refrigerate it unbaked. Pull it from the fridge while the oven preheats so it’s not going in ice cold, and add about 5 extra minutes to the bake time to account for the colder start.

How to Serve, Store & Customize This Recipe

Serving:

Slice the casserole into squares and serve it warm, straight from the baking dish.

A few slices of avocado or a spoonful of sour cream on the side rounds it out nicely, and it pairs well with hash browns or a bowl of fresh fruit if you’re feeding a crowd.

Storage:

Let leftovers cool completely before transferring them to an airtight container in the fridge, where they’ll keep for up to 4 days.

The eggs firm up a bit more once chilled, though a quick reheat in the microwave or a 325°F oven brings back most of the original texture. You can also freeze individual slices wrapped tightly for up to 2 months.

Customization:

Swap the ham for cooked breakfast sausage or crumbled bacon if that’s what you have on hand, or skip the meat entirely and add sauteed mushrooms for a vegetarian version.

Pepper jack or a Mexican cheese blend works well in place of cheddar if you want more heat, and a diced jalapeno mixed in with the bell peppers kicks things up further.

Oven Baked Denver Omelette Casserole

Course: Recipes

Servings

servings

Prep time

minutes

Cooking time

minutes

Calories

300

kcal

Ingredients

12 large eggs
1/2 cup whole milk
1 1/2 cups diced cooked ham
1 cup diced green bell pepper
3/4 cup diced red bell pepper
1/2 cup diced yellow onion
2 cups shredded cheddar cheese, divided
1 tablespoon butter, for the pan and skillet
1/2 teaspoon salt
1/4 teaspoon black pepper

Directions

Preheat the oven to 375°F and grease a 9×13 baking dish with butter.
Saute the peppers and onion in butter for about 5 minutes until soft.
Whisk the eggs with milk, salt, and pepper until frothy.
Layer the ham, vegetables, and half the cheese, then pour the eggs over top.
Top with the remaining cheese and bake 30 to 35 minutes until set.
Rest for 5 to 10 minutes before cutting into squares.
Slice and serve warm.

Notes

Sauté the bell peppers and onions before adding them to the casserole. This removes excess moisture and keeps the eggs from becoming watery.
Use freshly grated cheese for smoother melting and better flavor.
For extra protein, replace part of the milk with cottage cheese or add extra egg whites.
Avoid overbaking. Remove the casserole when the center is set but still slightly soft, as the eggs will continue cooking while it rests.
Let the Denver omelette casserole rest for 5–10 minutes before slicing.
Prepare the casserole the night before, cover it tightly, and refrigerate. Bake it the next morning, adding a few extra minutes if it is cold.
Store leftovers in an airtight container for up to four days. Reheat individual slices in the microwave or air fryer.