Ingredients:

  • 3 large Sweet Potatoes (Orange Variety, approx. 750g / 1.6 lbs), peeled and sliced 3mm thin
  • 2 medium Russet or Maris Piper Potatoes (approx. 400g / 14 oz), peeled and sliced 3mm thin
  • 15g (1 tbsp) Unsalted Butter, plus extra for greasing
  • 240 ml (1 cup) Heavy Cream (35% fat)
  • 120 ml (½ cup) Chicken or Vegetable Stock (Low Sodium)
  • 2 large cloves Garlic, finely minced
  • 1 tbsp Fresh Thyme leaves
  • ⅛ tsp freshly grated Nutmeg
  • 1 ½ tsp Fine Sea Salt (separated)
  • ½ tsp Freshly Ground Black Pepper
  • 100g (4 oz) Gruyère Cheese (or mature Cheddar), coarsely grated

Instructions:

  1. Preheat the oven to 190°C / 375°F (170°C fan/gas mark 5). Generously butter the entire interior of a 9x13 inch shallow baking dish.
  2. Using a mandoline or sharp knife, slice both the sweet potatoes and standard potatoes to a consistent 3mm (1/8 inch) thickness. Keep the sliced varieties separate.
  3. In a small saucepan, melt the 15g of butter over medium-low heat. Add the minced garlic and sauté gently for 30 seconds until fragrant (do not let it brown). Remove from heat.
  4. Whisk in the heavy cream, stock, thyme leaves, 1 tsp of salt, black pepper, and grated nutmeg until fully combined. The consistency should be thin and pourable.
  5. Take the sweet potato slices and lay them, slightly overlapping (like roof tiles), across the bottom of the prepared dish, filling the entire base. Sprinkle this layer lightly with the reserved ½ tsp of salt.
  6. Arrange the standard potato slices over the sweet potato layer, maintaining the overlapping pattern. Continue alternating layers of sweet potato and standard potato until all slices are used, ensuring a light sprinkle of salt is used every 2-3 layers for seasoning depth.
  7. Slowly pour the prepared cream mixture evenly over the entire layered potato stack. Gently shake the dish to ensure the liquid penetrates down to the bottom layer.
  8. Cover the dish tightly with aluminium foil and bake for 30 minutes. This steaming period ensures the potatoes soften completely.
  9. Remove the foil. Sprinkle the grated Gruyère evenly over the top layer. Return the dish to the oven and bake for another 25–30 minutes, or until the top is golden brown, bubbly, and a sharp skewer inserted into the centre slides in easily.
  10. Remove the Tian from the oven and let it rest on a wire rack for 10 minutes before serving. This allows the sauce to set and prevents the dish from collapsing.