Ingredients:

  • 3 large sweet potatoes (approx. 1.2 kg), peeled and uniform in size
  • 1 cup (240 ml) heavy cream (full-fat is best)
  • 1 large egg, lightly beaten
  • 1 Tbsp (5g) fresh sage leaves, finely chopped
  • 1 garlic clove (5g), finely minced
  • 1/4 tsp (1 ml) freshly grated nutmeg
  • 1 tsp (5 g) kosher salt, plus more for seasoning
  • 1/2 tsp (2.5 ml) black pepper, freshly cracked
  • 4 oz (115 g) Gruyère cheese, freshly grated
  • 1 Tbsp (15 g) unsalted butter, melted (for greasing the dish)

Instructions:

  1. Preheat oven to 375°F (190°C). Grease a shallow baking dish (approx. 9x13 inch) generously with melted butter and set aside.
  2. Peel the sweet potatoes. Using a mandoline or very sharp knife, slice the potatoes into thin, uniform rounds, approximately 1/8 inch (3 mm) thick. Toss the sliced potatoes in a large bowl with a pinch of salt and pepper for light seasoning.
  3. Make the Custard Base: In a medium bowl, whisk together the heavy cream, the beaten egg, chopped fresh sage, minced garlic, freshly grated nutmeg, 1 tsp salt, and black pepper.
  4. Assembly (The Shingle): Begin layering the sweet potato slices in the prepared dish, starting from one corner and overlapping them like roof tiles. Work your way across the entire dish in tight, neat rows, ensuring uniform coverage.
  5. Add the Custard and Topping: Slowly and evenly pour the cream mixture over the entire dish. Gently wiggle the dish to ensure the liquid settles completely between all the slices. Sprinkle three-quarters of the grated Gruyère cheese evenly over the potatoes.
  6. Initial Bake (Covered): Cover the dish tightly with foil or parchment paper. Bake for 30 minutes at 375°F (190°C). This steams the potatoes, ensuring they cook through evenly.
  7. Finish Bake (Uncovered): Remove the foil. Sprinkle the remaining Gruyère cheese over the top. Increase the oven temperature to 400°F (200°C) and bake for another 25–30 minutes, or until the top is deeply golden brown and a knife inserted into the center meets no resistance.
  8. Crucial Resting Step: If the top browns too quickly, loosely tent it with foil again. Once fully cooked, remove the Sweet Potato Tian from the oven. Let the dish rest on a wire rack for 10 minutes before slicing and serving. This allows the creamy custard to set and maintains the structural integrity of the layers.