Broccoli Au Gratin with white cheddar cheese is the perfect delicious side dish for the holidays! It uses frozen broccoli so is quick and easy to put together and pop in the oven! An elegant Thanksgiving, Easter or Christmas vegetable dish that can be made ahead and prepped in just 15 minutes!
With all the cooking and baking that comes with the holidays, this quick and easy Broccoli Au Gratin is the best green vegetable side dish to lighten your workload! Frozen broccoli and dried spices makes for no chopping! Plus it can be made ahead and baked the next day!
This frozen broccoli casserole is rich and creamy, while the broccoli stays tender but not mushy! It's a gorgeous dish for your holiday table!
Ingredients & Substitutions
This broccoli au gratin with frozen broccoli uses clean and simple ingredients that bring incredibly delicious flavor!
- Butter & Flour - Equal amounts of butter and flour are whisked together to form a roux. This is the thickener for the milk that will form the creamy sauce.
- Milk - Use whole milk if you can, or at least 2%. If all you have is skim, it would be great to substitute a splash of heavy cream. The milk is whisked into the roux, thickening it into a bechamel, a basic white sauce that will be the base of the gratin.
- Dried Spices - No need to chop fresh onion and garlic, these simple pantry dried spices boldly flavor your sauce. If you have it, use fresh thyme leaves, otherwise dried is fine. Fresh herbs are nice to garnish the finished dish!
- Salt & Pepper - Don't underestimate the importance of salt and pepper. They enhance the flavors of the sauce and season the broccoli.
- White Cheddar Cheese - An affordable, melty cheese, white cheddar brings this dish together! You can substitute gruyere cheese, common and delicious in au gratins, but much more expensive.
- Parmesan Cheese - Adds flavor and gives you a nice golden crusty topping.
- Frozen Broccoli Florets - I chose frozen broccoli over fresh for this recipe for a few reasons. For one, it's just so fast and easy! No need to thaw or chop, just toss it in frozen with the sauce and bake it! Frozen broccoli is already blanched, which means it is pre-cooked, making this dish bake up perfectly in less time. You could substitute the frozen broccoli and cauliflower mixture for a variation.
- Panko Bread Crumbs - Adding bread crumbs with the cheesy topping gives this broccoli au gratin its signature browned golden beauty! You can even make your own breadcrumbs by chopping and pulsing a bun or any bread from your freezer in the food processor! Use panko or make your own but avoid the regular, completely powdery breadcrumbs. They won't give you the right texture.
See recipe card for quantities.
This broccoli au gratin couldn't be easier! You will make a bechamel, a simple white sauce, on the stovetop with butter, flour and milk. Then toss it with the broccoli, top it with cheese and bake it in the oven!
Step 1 - Melt the butter in a skillet over medium low heat and whisk in the flour for about 1 minute to form a roux.
Step 2 - Whisk in the milk, it will thicken as it cooks. Whisk often for about 10 minutes. Keep at a simmer, don't boil.
Step 3 - When your bechamel sauce is thickened enough to coat the back of a spoon, turn off the heat.
Step 4 - Add in the seasonings and half the cheese and whisk until creamy.
Step 5 - Add the frozen broccoli, no need to thaw. Mix until well combined.
Step 6 - Transfer the mixture to a buttered baking dish.
Step 7 - Sprinkle evenly with the remaining cheese and then the bread crumbs.
Step 8 - Bake at 400° for 20 to 30 minutes or until hot, bubbly and golden. You can broil the top for a few minutes if you want it darker.
- Make Ahead Instructions - You can assemble this dish unbaked a day in advance, wrap in foil and keep in the fridge. Let it sit on the counter a half hour or so before baking to take the chill off.
- Travel Instructions - If you are headed to a holiday party, you can bake the gratin at home, cover it with foil and a dish towel and transport it in an insulated bag. Then just keep it warm in the hosts oven when you get there.
- Finding the right dish - When deciding what dish to use, you may want to dump your frozen broccoli into the empty dish to eyeball the amount. A large 9x13 casserole dish, "a lasagna pan" as I call it, is probably too big. You could double the recipe, or make 1.5 if feeding more people.
- Frozen Broccoli - I used 2 10 ounce bags of frozen broccoli florets for this dish to serve 6 to 8 people. I think it's worth buying a decent organic brand since sometimes cheap frozen broccoli gives you way more stems than florets.
- Don't skimp on the fat! - A half stick of butter may seem like a lot, but combined with the flour, it becomes the thickening agent for the sauce. Same for the milk, whole milk will make your sauce rich and creamy. If you only have skim milk, subbing a half a cup of the milk with heavy cream or half & half will help increase the fat.
- Shred your own Cheese - A block of white cheddar cheese is better quality and will melt and brown nicer than the pre-shredded packages. Pre-shredded cheese usually has an anti-clumping agent that makes them not melt into the sauce as well. Plus, a block of cheese is usually cheaper, especially when you consider how often the bottom end of a packet goes bad and ends up in the trash!
- Storage - Leftovers can be refrigerated in an airtight container for up to 4 days.
What to Serve With
Broccoli Au Gratin is the perfect green vegetable side dish for Thanksgiving, Easter or any of the holidays! You may also like Roasted Carrots and Brussel Sprouts and a holiday salad like this Blueberry Goat Cheese Salad with Candied Pecans.
- Add a starch like my Rosemary Garlic Mashed Potatoes or Maple Roasted Butternut Squash. These side dishes are perfect to accompany any main course including turkey, ham, or beef! Try this Raisin Pine Nut Goat Cheese Appetizer dip too!
- Weeknight Side Dish! - Broccoli Au Gratin is fancy and elegant, but is simple enough for a weeknight vegetable! Serve it with Whole Roasted Chicken, Shaved Pork Roast Sandwiches, Simply Perfect Beef Roast, or Salmon with Garlic Honey Butter.
You do not need to thaw the frozen broccoli for this recipe. Simple stir it into the bechamel sauce and bake. This makes it far easier than using fresh broccoli!
You can, but you will need to blanch or steam it first. This is why frozen broccoli is easier and just as good! If using fresh broccoli, wash it well, chop it into florets, and drop it into boiling salted water for about 4 minutes. Drain well before adding to the sauce.
Yes! To make Broccoli Au Gratin gluten-free, substitute a gluten-free flour and either omit or use a gluten-free panko for the bread crumb topping.
A bechamel sauce is a classic French white sauce made from melted butter and flour, a roux, used to thicken milk. Whisk together the butter and flour for about a minute over medium low heat and then whisk in the milk. Let it simmer for about 10 minutes. You'll want to whisk it often, and keep it at a simmer but not a boil. This should be enough time to thicken your sauce, however the longer you cook it the more it will reduce and thicken. It should be seasoned with salt and then can be used in many ways. Adding shredded cheese will also thicken the sauce further.
More Vegetable Side Dish Recipes
If you made this recipe, I'd love to hear how you liked it! Be sure to leave a star rating by clicking the stars in the recipe card, or leave a comment below!
Broccoli Au Gratin
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- 4 Tablespoons butter
- 4 Tablespoons flour
- 2 cups whole milk
- ½ teaspoon garlic powder
- ½ teaspoon onion powder
- ½ teaspoon dried or fresh thyme
- ½ teaspoon kosher salt
- 10 grinds fresh black pepper
- 2 cups white cheddar cheese (divided) shredded
- ½ cup Parmesan cheese (divided) grated
- 8 cups frozen broccoli florets (about 20 ounces)
- ½ cup panko bread crumbs
- Preheat the oven to 400° F.
- Use a bit of the butter to coat the baking dish. Then melt the rest in a large saucepan over medium low heat. Add the flour and whisk together for 1 minute until bubbly, forming a roux.
- Add the milk, whisking it together. Whisk it often for about 10 minutes while the sauce thickens. It can simmer a bit but do not boil.
- When the sauce has thickened enough to coat the back of a spoon, add the seasonings, salt, pepper, garlic powder, onion powder and thyme.
- Turn off the heat, and whisk in half the cheese. Add the broccoli and toss to coat.
- Pour the broccoli mixture into the prepared baking dish, top it with the rest of the cheese and the breadcrumbs.
- Bake at 400℉ uncovered for 20 to 30 minutes until hot and bubbly. You can broil it a few minutes if you'd like the cheese and breadcrumbs darker.
- Allow to rest about 5 minutes and serve!
- Serve broccoli au gratin in the same dish it is baked in, wrapping a towel around the base since it will be hot from the oven!
- Make Ahead - This dish can be fully assembled a day ahead and kept unbaked in the fridge, wrapped with foil. Let it sit on the counter a half hour or so before baking to take the chill off.
- Shred your own cheese for the best quality.
- Use whole milk, or if using skim milk, substitute half a cup of the milk with heavy cream or half & half.
- Use panko or make your own bread crumbs. Even a frozen bun or slice of bread chopped and pulsed in a food processor makes great bread crumbs! Avoid the fully ground powdery bread crumbs.