Sweet Potato Gratin Layers (Printable Version)

# What You'll Need:

→ Dairy and Butter

01 - 45 g unsalted butter, softened, divided, plus extra for greasing
02 - 240 ml heavy cream
03 - 180 ml whole milk
04 - 60 g grated Parmesan cheese, divided
05 - 240 g shredded Gruyère cheese, divided
06 - 2 large eggs

→ Vegetables and Herbs

07 - 900 g sweet potatoes (mix of purple, orange, and white), peeled and sliced 3 mm thick
08 - 12 g fresh thyme leaves, chopped, plus extra for garnish
09 - 5 g fresh sage leaves, chopped
10 - 12 g garlic cloves, chopped

→ Spices and Seasonings

11 - 1/4 tsp ground cinnamon
12 - 1/4 tsp ground nutmeg
13 - Kosher salt, to taste
14 - Freshly ground black pepper, to taste

# Step-by-Step Directions:

01 - Preheat the oven to 190°C. Butter a 2-quart casserole dish with 15 g unsalted butter.
02 - Melt 30 g butter in a small saucepan over medium heat. Once the butter stops foaming, add garlic and cook, stirring, until fragrant, about 30 seconds. Stir in thyme, sage, and 1/2 teaspoon kosher salt. Cook for another 30 seconds until herbs are warmed through.
03 - Add heavy cream, milk, cinnamon, and nutmeg to the saucepan. Bring to a simmer without boiling and cook, stirring occasionally, until slightly thickened, approximately 5 minutes. Remove from heat.
04 - In a medium bowl, beat the eggs. Gradually whisk 240 ml of the warm cream mixture into the eggs a few tablespoons at a time to temper them. Return the tempered egg mixture to the remaining cream in the saucepan and whisk until combined. Stir in 30 g Parmesan cheese and season with freshly ground black pepper.
05 - Place a layer of sweet potato slices in the bottom of the prepared dish, slightly overlapping and seasoning with a pinch of salt. Top with 160 g Gruyère cheese and 160 ml of the cream mixture. Repeat the layering process three more times, finishing with the cream mixture. Sprinkle the remaining 15 g Parmesan cheese on top.
06 - Butter a piece of aluminum foil and cover the dish tightly. Bake for 30 minutes.
07 - Remove the foil and continue baking until the sides are bubbling and the top is golden brown, about 30 minutes more. Garnish with fresh thyme before serving.

# Helpful Notes:

01 - Use a mandoline slicer or a sharp knife to achieve uniform 3 mm-thick slices for even cooking. Smaller sweet potato ends can be placed at the bottom layers to prevent waste.
02 - Sweet potato gratin can be assembled a day in advance and refrigerated either baked or unbaked. If baked ahead, cool completely and cover tightly before refrigerating up to three days.
03 - Leftovers keep refrigerated for 3 to 4 days or frozen for up to three months. Reheat in a 190°C oven until warmed through, approximately 20 minutes.

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