Ingredients:

  • 60 g (½ cup) All-Purpose Flour
  • 50 g (¼ cup, packed) Light Brown Sugar (for streusel)
  • 1 tsp Ground Cinnamon
  • ½ tsp Fine Sea Salt (for streusel)
  • 55 g (4 tbsp) Unsalted Butter, chilled and cubed (for streusel)
  • 60 g (½ cup) Pecans, roughly chopped
  • 3 large Sweet Potatoes (approx. 1.2 kg total), peeled
  • 60 g (4 tbsp) Unsalted Butter, softened (for greasing the dish)
  • 120 g (¾ cup) Dried Cranberries
  • 360 ml (1½ cups) Heavy Cream
  • 120 ml (½ cup) Whole Milk
  • 75 g (⅓ cup, packed) Light Brown Sugar (for custard)
  • 1 tbsp Pure Vanilla Extract
  • 1 tsp Fine Sea Salt (for custard)
  • ½ tsp Freshly Grated Nutmeg
  • ¼ tsp Ground Black Pepper

Instructions:

  1. Preheat oven to 190°C (375°F). Grease a 9x13 inch baking dish generously with softened butter.
  2. Make the Streusel: In a medium bowl, combine the flour, 50g brown sugar, cinnamon, and salt. Cut in the cold butter until the mixture resembles coarse crumbs. Stir in the chopped pecans. Place the streusel mixture in the fridge to chill.
  3. Slice the Sweet Potatoes: Peel the sweet potatoes. Using a mandoline (set to ⅛ inch / 3mm thickness) or a sharp knife, slice the potatoes into thin, uniform rounds. Consistency is key here.
  4. Prepare the Cream Custard: In a separate bowl, whisk together the heavy cream, milk, 75g brown sugar, vanilla extract, salt, nutmeg, and black pepper until the sugar dissolves completely.
  5. Assemble the Gratin: Arrange a layer of sliced sweet potatoes slightly overlapping in the prepared baking dish, covering the base. Scatter about one-third of the dried cranberries evenly over the potato layer. Repeat the layering process two more times (potatoes, then cranberries).
  6. Gently pour the cream custard evenly over the entire gratin, ensuring the liquid seeps into the spaces between the potato slices.
  7. Bake Covered: Cover the baking dish tightly with aluminium foil and bake for 35 minutes at 190°C (375°F). This ensures the potatoes steam and soften fully.
  8. Bake Uncovered: Remove the foil. Increase the oven temperature to 200°C (400°F). Bake uncovered for another 10–15 minutes, or until the top layer is lightly browned and the cream is bubbling.
  9. Apply Streusel: Remove the dish from the oven. Sprinkle the chilled pecan streusel evenly over the top layer. Return the gratin to the oven and bake for a final 5–10 minutes, or until the streusel is golden brown and crisp.
  10. Rest and Serve: Remove the gratin from the oven. Allow the dish to rest for 15 minutes before serving. This allows the custard to set up fully, preventing a messy, liquidy outcome.