Sweet Potato Gratin Dish (Print-Friendly Version)

Layers of sweet potatoes, cheese, and herbs baked to golden, creamy perfection for a cozy side.

# What You'll Need:

→ Dairy & Fats

01 - 45 g unsalted butter, softened, divided, plus additional for greasing
02 - 240 ml heavy cream
03 - 180 ml whole milk
04 - 75 g grated Parmesan cheese, divided
05 - 240 g shredded Gruyère cheese, divided

→ Produce & Herbs

06 - 8 g cloves garlic, finely chopped
07 - 10 g fresh thyme leaves, chopped, divided
08 - 5 g fresh sage leaves, chopped
09 - 900 g sweet potatoes (mix of purple, orange, and white), peeled and sliced 3 mm thick

→ Spices & Seasonings

10 - 1/4 tsp ground cinnamon (approximately 0.5 g)
11 - 1/4 tsp ground nutmeg (approximately 0.5 g)
12 - Kosher salt, to taste
13 - Freshly ground black pepper, to taste

→ Eggs

14 - 2 large eggs

# How to Make It:

01 - Preheat oven to 190°C. Grease a 2-quart casserole dish with 15 g softened butter.
02 - Melt 30 g butter in a small saucepan over medium heat until foaming ceases. Add chopped garlic and cook for 30 seconds until fragrant. Stir in thyme, sage, and 1/2 teaspoon salt; cook for an additional 30 seconds to release aromas.
03 - Add heavy cream, whole milk, ground cinnamon, and nutmeg to the saucepan. Bring mixture to a gentle simmer, avoiding boiling, and cook for 5 minutes until slightly thickened. Remove from heat.
04 - In a bowl, beat eggs lightly. Gradually whisk 240 ml of the warm cream sauce into eggs, adding a few tablespoons at a time to temper. Return egg mixture to the saucepan with remaining cream, whisk to combine, then stir in 60 g Parmesan cheese. Season with freshly ground black pepper.
05 - Arrange a layer of sweet potato slices at the bottom of the dish, slightly overlapping. Season lightly with salt. Sprinkle 160 g shredded Gruyère over potatoes, then pour 160 ml of the cream sauce over the layer. Repeat layering three more times, finishing with the cream sauce on top. Sprinkle the final 15 g Parmesan evenly over the surface.
06 - Butter a sheet of aluminum foil and cover the dish tightly. Bake for 30 minutes at 190°C.
07 - Remove foil and continue baking an additional 30 minutes until the gratin is bubbling and golden brown at the edges. Garnish with remaining thyme leaves before serving.

# Additional Tips:

01 - Use a mandoline or a sharp knife to achieve uniform 3 mm slices. Small end pieces can be layered at the bottom to minimize waste.
02 - Make ahead by assembling and baking, then refrigerate wrapped for up to 3 days. Alternatively, assemble without baking and refrigerate for up to 2 days.
03 - Store leftovers in an airtight container in the refrigerator for 3–4 days or freeze for up to 3 months. Reheat at 190°C for approximately 20 minutes.

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