The first time I made this spinach gratin was for a holiday dinner several years ago. I was looking for a side dish that would feel special but not overshadow the main course. What started as an experiment has become one of my most requested recipes—especially from friends who claim they “don’t like spinach.” There’s something about the creamy sauce and golden cheese crust that transforms humble spinach into something truly magnificent.

I’ve tweaked this recipe countless times in my kitchen, adjusting the cheese blend, perfecting the sauce consistency, and finding that sweet spot where comfort meets elegance. What I love most is watching skeptics take that first reluctant bite, only to reach for seconds minutes later.

The Magic of Transformation

What makes this gratin special is the balance between the earthy spinach and the velvety béchamel sauce. I’ve learned through many test batches that removing excess moisture from the spinach is absolutely crucial—it’s the difference between a silky gratin and a watery disappointment.

The combination of Parmesan in the sauce and Monterey Jack (or Gruyere, when I’m feeling fancy) on top creates layers of flavor that elevate this beyond a simple vegetable side dish. I’ve served this at casual Sunday dinners and holiday feasts alike, and it always feels right at home.

What You’ll Need

Unsalted butter: This creates the base for our béchamel sauce; I prefer unsalted so I can control the seasoning.

Yellow onion: Finely diced for a subtle sweetness that mellows as it cooks. I’ve tried red onions, but yellow gives a more delicate flavor that complements the spinach better.

Garlic: Just one clove, minced—enough to enhance without overpowering. Sometimes I’ll add two if cooking for my garlic-loving friends.

All-purpose flour: The thickening agent for our sauce; make sure to cook it briefly with the butter to remove any raw flour taste.

Milk: Creates the creamy base of our sauce. I typically use whole milk for richness, but 2% works nicely too if that’s what you have on hand.

Kosher salt: The larger crystals dissolve beautifully in the sauce. I’ve found that table salt can sometimes make the dish taste too sharp.

Nutmeg: Just a whisper transforms the sauce. I keep whole nutmegs by my stove and grate them fresh, but pre-ground works perfectly well too.

Frozen chopped spinach: My kitchen workhorse! I’ve made this with fresh spinach too, but frozen is more consistent and much less work.

Parmesan cheese: Adds a salty depth to the sauce itself. I prefer freshly grated, but pre-grated will work in a pinch.

Black pepper: Freshly ground gives the best flavor.

Monterey Jack or Gruyere cheese: For that irresistible golden top. Monterey Jack creates a mild, crowd-pleasing finish, while Gruyere adds a nutty sophistication that I love for special occasions.

Let’s Get Cooking

Creating the Base

I start by preheating my oven to 400 degrees and lightly coating my favorite 2-quart casserole dish with cooking spray. This dish was a housewarming gift years ago and has been the vessel for countless gratins since.

In my large skillet over medium heat, I melt the butter until it foams slightly, then add the diced onions. Patience is key here—I cook them for 3-4 minutes until they’re translucent but not browned. When they’re soft and fragrant, I add the minced garlic and cook for just one more minute. Garlic burns easily, and there’s nothing worse than bitter garlic flavor ruining your sauce.

Building the Sauce

Now for the transformation! I sprinkle the flour over the onion mixture and stir constantly for a full minute. This step cooks out the raw flour taste while creating the foundation for our silky sauce. After the minute is up, I pour in the milk and add the salt and nutmeg, stirring to combine everything.

Once the liquid comes to a gentle bubble, I reduce the heat to low and let it simmer for 10 minutes. This is when I usually set the table or prep other dishes, returning every minute or so to give it a good stir. The sauce will gradually thicken into a velvety consistency that coats the back of a spoon.

The Spinach Secret

This next step is absolutely critical—and I learned it the hard way after serving a watery gratin at one of my first dinner parties. I squeeze as much liquid as possible from the defrosted spinach. Sometimes I’ll even wrap it in a clean kitchen towel and twist until my hands ache. Trust me, this extra effort makes all the difference!

Once the spinach is properly dried, I add it to the sauce along with the Parmesan cheese, stirring until everything is beautifully combined. This is when I taste and adjust the seasoning, sometimes adding an extra pinch of salt or pepper.

Golden Finish

The final touch is transferring this vibrant green mixture to my prepared baking dish and sprinkling the top with Monterey Jack or Gruyere cheese. I slide it into the oven and bake for 28-30 minutes, until the cheese turns golden and the edges bubble invitingly.

I often take pictures of the finished gratin by my dining room window, where the afternoon light catches the golden cheese top perfectly. But I have to work quickly—this dish doesn’t stay intact long once my family catches the aroma!

Make It Your Own

Mediterranean Variation: Last summer, I experimented with adding a handful of chopped marinated artichoke hearts and a sprinkle of crumbled feta on top. The briney notes complemented the creamy spinach beautifully.

Holiday Elegance: For Christmas dinner last year, I added a pinch of cayenne to the sauce and replaced the top cheese with a mixture of Gruyere and breadcrumbs tossed with a little melted butter. The slight heat and extra crunch elevated it for the special occasion.

Weeknight Simplification: On busy weeknights, I sometimes use pre-made white sauce from the refrigerated section of my grocery store. It’s not quite as flavorful as homemade, but with good cheese and properly dried spinach, it still makes a lovely quick side dish.

My Best Tips

The Squeeze Test: When you think you’ve removed enough liquid from your spinach, squeeze again! I can usually get another quarter cup of liquid out when I think I’m done.

Sauce Consistency: The béchamel should be the consistency of heavy cream before you add the spinach. If it’s too thick, add a splash more milk; if too thin, let it simmer a few minutes longer.

Cheese Shield: If your top is browning too quickly but the gratin isn’t heated through, loosely cover with foil for the remaining baking time.

Make-Ahead Magic: I often prepare this through the sauce stage up to two days ahead, then add the spinach and cheese just before baking. Perfect for busy entertaining days!

Frequently Asked Questions

Can I use fresh spinach instead of frozen? → You can, though you’ll need about 3-4 pounds to equal the 50 ounces of frozen. Blanch it quickly, cool in ice water, then squeeze dry.

Is there a dairy-free version? → I’ve made this with unsweetened almond milk and dairy-free cheese for my lactose-intolerant friend. The texture is slightly different, but still delicious.

How do I know when it’s done? → The edges should be bubbling, the top golden, and if you insert a knife in the center, it should come out hot to the touch.

Can I freeze leftovers? → Yes! Portion into airtight containers and freeze for up to 3 months. Thaw in the refrigerator overnight before reheating in a 350-degree oven until hot throughout.

What can I serve with this? → I love pairing this with a simply roasted chicken or grilled steak. It also works beautifully alongside a roast for holiday meals.

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