Golden, bubbling gratin is the definition of French comfort food. This French cauliflower and broccoli gratin marries tender florets with a silky Mornay sauce, crowned with nutty Gruyère. It’s the perfect way to elevate humble vegetables into a show‑stopping side—or a vegetarian main. Let me show you how, step by step.
See also: my classic béchamel sauce guide for extra tips. Learn more about Gruyère cheese varieties to choose the best block for grating.
Why You’ll Love This Recipe
Authentic French technique: classic béchamel upgraded to a cheese‑laden Mornay.
Family‑friendly: a sneaky, tasty way to eat more greens.
Make‑ahead friendly: assemble, chill, then bake when needed.
Ingredients (Serves 4–6)
1 small head cauliflower, cut into bite‑size florets (about 500 g)
1 small head broccoli, cut into bite‑size florets (about 400 g)
A few cubes of sweet potatoes (about 150 g), peeled and diced — optional, added for extra sweetness and texture
40 g unsalted butter
40 g plain flour
500 ml whole milk, warmed
80 g grated Gruyère (reserve 20 g for topping)
40 g grated Parmesan
Pinch freshly grated nutmeg
½ tsp fine sea salt, plus more for blanching water
Freshly ground black pepper
1 tbsp breadcrumbs (optional, for extra crunch)
Optional: bacon strips (see Variations)
Step‑by‑Step Instructions
Blanch the vegetables
• Bring a large pot of salted water to a rolling boil.
• Add cauliflower; cook 3 minutes. Add broccoli; cook 2 minutes more.
• Drain and plunge into ice water to stop cooking. Drain again and pat dry.
• Tip: Slightly undercook—the oven will finish the job.
2. Make the Mornay sauce
• Melt butter in a medium saucepan over medium heat.
• Whisk in flour; cook 2 minutes to form a pale roux.
• Gradually pour in warm milk, whisking constantly until smooth and thick, 4–5 minutes.
• Stir in 60 g Gruyère and all the Parmesan until melted.
• Season with nutmeg, salt and pepper.
Note: Mornay sauce is simply béchamel sauce with cheese added.
3. Assemble
• Pre‑heat oven to 200 °C (180 °C fan) / 400 °F. Butter a 1.5 L gratin dish.
• Arrange cauliflower and broccoli evenly. Pour sauce over, nudging to coat every crevice.
• Sprinkle the reserved Gruyère (and breadcrumbs, if using) on top.
4. Bake
• Bake 20–25 minutes until bubbling and deeply golden.
• Let stand 5 minutes, then serve piping hot.
Variations & Substitutions
Replace Gruyère with Comté or Emmental.
Swap half the milk for cream for extra indulgence.
Add a handful of lardons (cooked:optional) for a gratin savoyard twist.
Storage & Reheating
Cool leftovers, cover and refrigerate up to 3 days. Reheat at 180 °C / 350 °F for 15 minutes.
Frequently Asked Questions
Can I freeze the gratin?
Yes. Assemble but don’t bake, wrap tightly, and freeze up to 2 months. Bake from frozen at 180 °C / 350 °F for 45–50 minutes.
Can I make it gluten‑free?
Swap the flour for a 1:1 gluten‑free blend or cornstarch.
Bon appétit! If you tried this French cauliflower and broccoli gratin, leave a rating or comment below—je vous écoute!🥂
