Ingredients:

  • 5 large Sweet Potatoes (approx. 1.8 kg), peeled and sliced 1/8 inch (3 mm) thick
  • 1 cup (240 g) Fresh or Frozen Cranberries
  • 1 tbsp (15 g) Unsalted Butter (for greasing)
  • 1 ½ cups (360 ml) Heavy Cream (Double Cream)
  • ½ cup (120 ml) Whole Milk
  • 2 Large Eggs
  • ½ cup (100 g) Light Brown Sugar, packed (Custard)
  • 1 tsp (5 ml) Pure Vanilla Extract
  • 1 tsp (5 ml) Ground Cinnamon
  • ½ tsp (2.5 ml) Ground Nutmeg
  • ½ tsp (2.5 g) Kosher Salt
  • ¼ cup (30 g) All-Purpose Flour (Plain Flour)
  • ¼ cup (50 g) Light Brown Sugar, packed (Streusel)
  • 2 tbsp (30 g) Unsalted Butter, cold and cubed (Streusel)
  • ½ cup (60 g) Pecans, chopped

Instructions:

  1. Prep and Preheat the oven to 375°F (190°C). Generously butter the 9x13 inch baking dish. Peel and slice the sweet potatoes uniformly, aiming for a thickness of 1/8 inch (3 mm). A mandoline is highly recommended for uniform slicing.
  2. Prepare the Streusel Topping: In a small bowl, combine the flour, brown sugar (streusel portion), and cold butter. Use your fingertips to quickly work the butter into the dry ingredients until coarse crumbs form. Stir in the chopped pecans and set aside in the fridge.
  3. Create the Spiced Custard Base: In a saucepan, gently heat the heavy cream and milk over medium heat until small bubbles form around the edge (do not boil). Remove immediately from the heat. In a separate large bowl, whisk together the eggs, brown sugar (custard portion), vanilla, cinnamon, nutmeg, and salt.
  4. Tempering: Slowly pour the warm cream mixture into the egg mixture while continuously whisking. Strain the entire custard mixture through a fine-mesh sieve into a jug to remove any potential lumps.
  5. Layer the Gratin: Arrange one-third of the sliced sweet potatoes in an even layer across the bottom of the prepared dish. Sprinkle half of the cranberries. Repeat the layering: another third of the potatoes, followed by the remaining cranberries. Finish with the final layer of sweet potatoes.
  6. Soak and Bake (Initial): Slowly pour the strained custard mixture over the layered potatoes. Press down gently to ensure the liquid is evenly distributed. Cover the baking dish tightly with aluminium foil and bake for 30 minutes at 375°F (190°C).
  7. Finish Baking: Remove the foil. Carefully sprinkle the chilled pecan streusel topping evenly over the potatoes. Return to the oven, uncovered, and bake for an additional 20–30 minutes, or until the topping is golden brown, the custard is set, and the potatoes are fork-tender.
  8. Rest: Allow the gratin to rest for 10 minutes before serving. This helps the custard firm up and prevents it from running when sliced.