Philly Cheesesteak Grilled Cheese Casserole

When two comfort food classics collide, something magical happens. My Philly Cheesesteak Grilled Cheese Casserole combines the savory, meaty goodness of a Philadelphia cheesesteak with the gooey, melty satisfaction of a grilled cheese sandwich—all in convenient casserole form!

This crowd-pleasing dish transforms traditional street food into a family-friendly dinner that’s perfect for weeknight meals. The tender beef, caramelized onions, and colorful peppers are layered between buttery bread and blankets of melted cheese for an irresistible comfort food experience that comes together in just 45 minutes.

Why You’ll Love This

• No flipping individual sandwiches—everything bakes together in one dish
• Perfect make-ahead option that reheats beautifully for lunches
• Customizable with your favorite cheesesteak toppings
• Kid-friendly while still sophisticated enough for adults
• Great for using up leftover steak or roast beef

Ingredients

• 9 oz thinly sliced roast beef
• 1 cup yellow onion, diced
• 1 cup green bell pepper, diced
• 0.87 oz brown gravy mix packet
• 1/2 cup water
• 12 slices white or whole wheat bread
• 1/2 cup margarine or butter, softened
• 4 cups shredded mozzarella cheese

Instructions

1. Preheat your oven to 400°F and grease a 9×13 inch baking dish. Chop the roast beef slices into bite-sized pieces – this makes it easier to eat and distributes the flavor better throughout the casserole.
2. Heat a large skillet over medium-high heat with a dab of butter or margarine. Add the chopped roast beef, diced onions, and green peppers. Cook everything together, stirring frequently, until the onions become translucent and the peppers start to soften – about 5-7 minutes.
3. Sprinkle the brown gravy mix over the beef and vegetables, then add the water. Stir everything together until the gravy coats all the ingredients evenly. This creates that rich, savory base that ties all the flavors together. Remove from heat and set aside.
4. Spread 1/4 cup of margarine on 6 slices of bread, then cut each slice in half. Place these pieces margarine-side down in a single layer in your greased baking dish. Sprinkle 2 cups of mozzarella cheese over the bread layer.
5. Spoon the roast beef mixture evenly over the cheese layer, spreading it out to cover the bread completely. Top with the remaining 2 cups of mozzarella cheese – this creates those amazing gooey, stretchy layers.
6. Spread margarine on the remaining 6 slices of bread and cut them in half. Place these pieces margarine-side up on top of the casserole in a single layer. Bake for 26-30 minutes until the top bread is golden brown and the cheese is bubbly.
7. Let the casserole rest for about 5 minutes before slicing – this helps it hold together better. Cut into squares and serve immediately while the cheese is still melted and gooey. This is comfort food at its finest!

Tips & Variations

For authentic Philly flavor, try using Cheez Whiz instead of or alongside the sliced cheeses. Want some heat? Add sliced jalapeños or a dash of hot sauce to the filling. You can also substitute the ribeye with chicken for a lighter option, or use plant-based meat alternatives for a vegetarian version.

To save time, prep the filling a day ahead and refrigerate until ready to assemble. For extra crispiness, brush the top bread slices with melted butter mixed with a pinch of garlic powder before baking.

Serving Suggestions

This hearty casserole pairs beautifully with a simple side salad dressed with vinaigrette to cut through the richness. For a more substantial meal, serve with crispy potato chips, pickle spears, or a cup of tomato soup for dipping. A cold beer or sparkling lemonade makes the perfect beverage companion.

Notes

This casserole can be assembled up to the baking step, covered, and refrigerated for up to 24 hours. Just add 5-10 minutes to the covered baking time if cooking from cold. Leftovers will keep in the refrigerator for up to 3 days and can be reheated in a 350°F oven until warmed through.

For best results, slice your steak as thinly as possible—partially freezing it for 15-20 minutes before slicing can help achieve those paper-thin cuts that are characteristic of authentic Philly cheesesteaks.

FAQs

Can I use a different type of bread?
Absolutely! Sourdough or Texas toast work wonderfully, just make sure it’s sturdy enough to hold up to the filling.

Is there a way to make this ahead for a party?
Yes! Prepare everything up to the baking step, cover tightly, and refrigerate. Bake just before serving.

What’s the best cheese to use for authentic flavor?
While provolone and American cheese are popular choices, many Philadelphia locals swear by Cheez Whiz for the most authentic experience.

Can I freeze this casserole?
You can freeze it unbaked for up to a month. Thaw completely in the refrigerator before baking as directed.

How do I know when it’s done baking?
The top should be golden brown, the edges crispy, and the cheese completely melted and bubbly when it’s ready.

Recipe by Nancy RH

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Servings8

Prep15 min

Cook30 min

Calories465 kcal

Ingredients

• 9 oz thinly sliced roast beef
• 1 cup yellow onion, diced
• 1 cup green bell pepper, diced
• 0.87 oz brown gravy mix packet
• 1/2 cup water
• 12 slices white or whole wheat bread
• 1/2 cup margarine or butter, softened
• 4 cups shredded mozzarella cheese

Steps

1. Preheat your oven to 400°F and grease a 9×13 inch baking dish. Chop the roast beef slices into bite-sized pieces – this makes it easier to eat and distributes the flavor better throughout the casserole.
2. Heat a large skillet over medium-high heat with a dab of butter or margarine. Add the chopped roast beef, diced onions, and green peppers. Cook everything together, stirring frequently, until the onions become translucent and the peppers start to soften – about 5-7 minutes.
3. Sprinkle the brown gravy mix over the beef and vegetables, then add the water. Stir everything together until the gravy coats all the ingredients evenly. This creates that rich, savory base that ties all the flavors together. Remove from heat and set aside.
4. Spread 1/4 cup of margarine on 6 slices of bread, then cut each slice in half. Place these pieces margarine-side down in a single layer in your greased baking dish. Sprinkle 2 cups of mozzarella cheese over the bread layer.
5. Spoon the roast beef mixture evenly over the cheese layer, spreading it out to cover the bread completely. Top with the remaining 2 cups of mozzarella cheese – this creates those amazing gooey, stretchy layers.
6. Spread margarine on the remaining 6 slices of bread and cut them in half. Place these pieces margarine-side up on top of the casserole in a single layer. Bake for 26-30 minutes until the top bread is golden brown and the cheese is bubbly.
7. Let the casserole rest for about 5 minutes before slicing – this helps it hold together better. Cut into squares and serve immediately while the cheese is still melted and gooey. This is comfort food at its finest!