Roasted Vegetable Gratin with Dijon Cheesy White Sauce & Panko Crunch

Tender roasted cauliflower, broccoli, pumpkin, carrot, and zucchini baked in a creamy Dijon cheese sauce with a golden, buttery panko topping.

Ingredients

• 3 cups cauliflower florets (about 350g)
• 3 cups broccoli florets (about 300g)
• 2 cups pumpkin, peeled and cut into 2.5cm / 1-inch cubes (about 350g)
• 2 medium carrots, sliced 5mm / 1/4-inch thick (about 200g)
• 1 medium zucchini, sliced 1cm / 1/2-inch thick (about 200g)
• 2 tbsp olive oil
• 1 1/2 tsp salt, divided
• 1/2 tsp black pepper, divided
• 4 tbsp butter
• 1/4 cup all-purpose flour
• 3 cups milk (warm is best)
• 1 tbsp Dijon mustard
• 1 1/2 cups shredded cheese (cheddar is ideal; any good melting cheese works), packed (about 150g)
• 1/4 tsp garlic powder (or 1 small garlic clove, finely minced)
• Pinch of nutmeg (optional but excellent)
• 1–2 tbsp water (only if needed to loosen)
• 1 cup panko breadcrumbs
• 2 tbsp butter, melted (or 2 tbsp olive oil)
• 1/4 cup shredded cheese (optional, for extra crunch and color)

Method

• 1

  Step 1: Roast the vegetables (for better flavor, less watery gratin)

  Preheat oven to **220°C / 425°F**. Toss cauliflower, broccoli, pumpkin, carrot, and zucchini with **2 tbsp olive oil**, **1 tsp salt**, and **1/4 tsp pepper**. Spread on two trays if crowded (crowding steams). Roast for **18–22 minutes**, tossing once halfway, until the pumpkin is tender and edges are browned.

• 2

  Step 2: Make the Dijon cheesy white sauce

  Reduce oven to **200°C / 390°F**. In a saucepan over medium heat, melt **4 tbsp butter**. Add **1/4 cup flour** and whisk constantly for **1 minute** until it smells slightly nutty (don’t let it brown). Slowly pour in **3 cups milk** while whisking until smooth. Cook, whisking, for **3–5 minutes** until thick enough to coat the back of a spoon. Whisk in **Dijon**, **garlic**, remaining **1/2 tsp salt** and **1/4 tsp pepper**, and nutmeg if using. Turn off heat, then stir in **1 1/2 cups cheese** until melted and silky. If it becomes too thick, loosen with **1–2 tbsp water**.

• 3

  Step 3: Assemble

  Lightly oil a **2.5–3L / 9x13-inch** baking dish. Tip in the roasted vegetables. Pour over the cheese sauce and gently toss to coat without breaking the veg too much (pumpkin gets soft).

• 4

  Step 4: Top with panko

  Mix **panko** with **melted butter** (and **1/4 cup cheese** if using). Sprinkle evenly over the gratin.

• 5

  Step 5: Bake until bubbly and golden

  Bake at **200°C / 390°F** for **12–15 minutes** until the edges are bubbling. Switch to **broil/grill** for **1–3 minutes** to toast the top deeply golden—watch closely (panko can go from golden to burnt fast). Rest **5 minutes** before serving so the sauce sets slightly.

Tips

• **Roasting matters:** It drives off moisture so your sauce stays creamy instead of watery—especially important with zucchini and broccoli.
• **Cheese options:** Cheddar is classic; any melting cheese works. If your cheese is mild, add an extra **1 tsp Dijon** for more punch.
• **Make-ahead:** Roast veg and make sauce up to **2 days ahead**. Assemble, refrigerate, then bake (add **5–10 minutes** since it’s cold).
• **Serving ideas:** Perfect with a simple green salad, or as a side to roast chicken. Leftovers reheat best covered in the oven at **180°C / 350°F** until hot.

Nutrition (per serving, estimate)