Ingredients:

  • 3 large Sweet Potatoes (approx. 1 kg / 2.2 lbs), peeled and uniformly sliced (1/8 inch / 3 mm thickness)
  • 1 Tbsp (15g) Unsalted Butter, softened (for greasing the dish)
  • 1 tsp (5g) Sea Salt
  • 1/2 tsp (2.5 ml) Black Pepper, freshly ground
  • 2 cloves Garlic, finely minced or grated
  • 1 Tbsp (5g) Fresh Thyme, leaves stripped from stems
  • 1 cup (240 ml) Double Cream (Heavy Cream)
  • 1/2 cup (120 ml) Whole Milk (Full-Fat)
  • 1/4 tsp (1.25 ml) Freshly Grated Nutmeg
  • 4 oz (115g) Gruyère Cheese, freshly grated (divided)

Instructions:

  1. Prepare the Oven and Dish: Preheat the oven to 375°F (190°C). Grease a 9x13 inch baking dish generously with softened butter.
  2. Slice the Sweet Potatoes: Peel the sweet potatoes. Using a mandoline or a very sharp knife, slice them into even 1/8-inch (3 mm) rounds. Do not rinse them—the residual starch helps bind the dish.
  3. Create the Cream Infusion: In a medium saucepan, combine the double cream, whole milk, minced garlic, thyme leaves, nutmeg, salt, and pepper. Gently heat over medium-low heat until tiny bubbles just begin to form around the edges. Do not allow the mixture to boil. Remove from heat immediately.
  4. Establish the First Layer: Arrange about one-third of the sweet potato slices in the prepared dish, slightly overlapping them like roof tiles. Ensure the bottom of the dish is fully covered.
  5. Add Seasoning and Cheese: Sprinkle a light layer of 3 oz of the grated Gruyère cheese over the potatoes. Ladle about one-third of the cream mixture evenly over the layer.
  6. Repeat Layers: Continue layering with the remaining sweet potatoes, cheese, and cream mixture, ending with a final layer of sweet potatoes that is soaked in the remaining cream. The top surface should be visibly wet.
  7. Apply Final Topping (Initial): Sprinkle the remaining 1 oz of Gruyère cheese evenly over the top layer.
  8. The Initial Bake (Covered): Cover the baking dish tightly with foil. Bake in the preheated oven for 40 minutes.
  9. The Second Bake (Uncovered): Remove the foil. Increase the oven temperature slightly to 400°F (200°C) if desired, and continue baking uncovered for another 15–20 minutes, until the potatoes are tender when pierced and the top is deeply golden brown and bubbling.
  10. The Crucial Rest: Remove the Tian from the oven. Allow it to rest uncovered on a wire rack for a minimum of 15 minutes before serving. This resting period is essential to allow the cream to firm up and set the dish.