Cauliflower Au Gratin

By Lily | Last modified on Mar 22, 2026

Featured in: Side Dishes

Cauliflower Au Gratin Recipe (keto casserole)

Indulge in all the comforting, cheesy goodness of a classic au gratin potato dish without the carbs! This Cauliflower Au Gratin delivers rich, creamy layers of tender cauliflower baked with Swiss Gruyere cheese and green onions, creating a luscious low-carb casserole that’s both satisfying and nutritious.

Perfect as a side or a main, this keto-friendly dish offers a delicious way to incorporate more vegetables into your meals while still enjoying bold flavors. Its golden, bubbly top and tender, creamy interior make it a crowd-pleaser for any occasion.

Why You’ll Love This Recipe

Low carb alternative to traditional potato au gratin, perfect for keto diets.
Uses Gruyere and Swiss cheeses which melt to create a rich, creamy sauce.
Simple ingredients and easy preparation for a comforting homemade casserole.
High in protein and flavor, making it both satisfying and healthy.

Ingredients

Cauliflower (1 head or 4 cups): Fresh cauliflower sliced thinly to replace potatoes and create tender layers.
Swiss Gruyere cheese (2 cups, shredded): Melts beautifully to make a creamy, flavorful cheese sauce; Swiss cheese is a fine substitute.
Green onions (4, sliced): Adds a mild onion flavor and fresh color throughout the dish.
Heavy cream (1 ½ cups): Provides rich creaminess for the casserole base and helps meld the cheese with cauliflower.
Salt and black pepper: Season to taste for balanced flavor that highlights the cheese and vegetables.
Cooking spray: Used to lightly grease the baking dish and prevent sticking.

Instructions

Preheat and Prepare Baking Dish: Start by heating your oven to 375°F to ensure an even baking temperature. Lightly spray an 8×10 inch casserole dish with cooking spray to keep the casserole from sticking and make cleanup easier.
Slice and Layer Cauliflower: Cut the cauliflower into thin, even slices for consistent cooking. Arrange about half the slices in an even layer in the prepared dish; layering helps create a structured casserole reminiscent of potato au gratin.
Add Cheese and Green Onions: Sprinkle half the shredded Gruyere cheese evenly over the first cauliflower layer. Then, scatter the sliced green onions on top to distribute flavor throughout. Season lightly with salt and fresh black pepper.
Add Remaining Cauliflower: Place the remaining cauliflower slices in a uniform layer over the cheese and onions. This layering is essential to balance the cheesy, creamy texture with tender cauliflower throughout the dish.
Pour Cream and Top with Cheese: Gently pour heavy cream evenly over all the layers to soak the casserole. Finish by covering with the remaining shredded cheese to create a golden, bubbly crust during baking.
Cover and Bake Initially: Cover the dish with foil to trap moisture, allowing the cauliflower to steam and soften without drying. Bake in the preheated oven for 30 minutes, which helps develop a tender texture inside.
Uncover and Brown: Remove the foil carefully and continue baking for an additional 40 minutes. This step lets the cheese brown and the top crisp, while the cauliflower becomes fork tender. Monitor occasionally for perfect doneness.
Rest Before Serving: Let the casserole sit for 5 minutes after baking to thicken the sauce and set the layers. This resting period improves texture and makes serving easier.

You Must Know

The baking time may vary depending on your oven and cauliflower thickness, so check periodically for doneness.
If you prefer a thicker sauce, try reducing cream to 1 cup but note it might be less saucy.
Fresh cauliflower yields the best texture; frozen or half-and-half may increase water content and alter sauce consistency.
Use at least an 8×10 inch baking dish to achieve proper layering and cooking results.

Storage Tips

Store leftovers in an airtight container in the refrigerator for up to 3 days. Reheat gently in the oven or microwave to maintain creaminess without drying out the casserole.

Serving Suggestions

Serve this Cauliflower Au Gratin alongside roasted meats or grilled fish for a comforting, low-carb meal. It also pairs wonderfully with fresh green salads or steamed vegetables for a well-rounded plate.

Professional Tips

Gruyere cheese combined with heavy cream forms a luscious sauce that distinguishes this dish from typical casseroles.
Using green onions adds subtle sharpness and freshness to balance the richness.
For a flavor twist, try substituting sharp cheddar cheese, but expect a slightly different taste profile.

FAQs

Can I use frozen cauliflower for this recipe?: Frozen cauliflower can be used but may release more water, impacting sauce thickness. Thaw and drain excess moisture before baking for best results.
What if I don’t have Gruyere cheese?: Swiss cheese is a good substitute and still melts well, creating a mild, creamy texture. Sharp cheddar can also be used for a bolder flavor.
Is this recipe suitable for a keto diet?: Yes! This low-carb recipe contains about 1.8 net carbs per serving, making it ideal for keto and low-carb lifestyles.
Can I prepare this dish ahead of time?: You can assemble the casserole a few hours ahead and refrigerate. Bake it fresh for best texture and flavor.
How do I know when the casserole is done?: The cauliflower should be fork tender, and the cheese topping golden brown and bubbly. Cooking times may vary, so check periodically.