Ingredients:

  • 5 lbs (2 kg) Russet or Yukon Gold Potatoes, peeled, sliced uniformly 1/8 inch (3 mm) thick
  • 1 Tbsp (15 g) Unsalted Butter, softened (for greasing)
  • 1 tsp (5 ml) Fresh Thyme leaves
  • 4 Tbsp (57 g) Unsalted Butter
  • 1 medium (50 g) Shallot or Small Onion, finely minced
  • 4 Tbsp (30 g) All-Purpose Flour (Plain)
  • 2 cups (480 ml) Whole Milk, warmed gently
  • 1 cup (240 ml) Heavy Cream (Double Cream)
  • 2 cloves Garlic, finely minced or pressed
  • 1 cup (100 g) Freshly Grated Gruyère or Mature Cheddar (Optional)
  • 1/4 tsp (1.2 ml) Fresh Nutmeg, freshly grated
  • 5 tsp (7.5 ml) Fine Sea Salt
  • 1/2 tsp (2.5 ml) Freshly Ground Black Pepper

Instructions:

  1. Preheat oven to 350°F (175°C). Peel the potatoes and use a mandoline or sharp knife to slice them into uniform 1/8 inch (3 mm) thick rounds. Rinse the sliced potatoes in cold water to remove excess starch, drain thoroughly, and pat dry. Generously grease the 9x13 inch baking dish with the reserved softened butter.
  2. Prepare the Roux: Melt the 4 Tbsp of butter in a heavy-bottomed saucepan over medium heat. Add the minced shallot and sauté gently for 3-4 minutes until translucent. Add the minced garlic and cook for 1 minute until fragrant. Sprinkle the flour over the mixture and whisk constantly for 1-2 minutes until a smooth paste (roux) forms.
  3. Make the Sauce: Gradually whisk in the warm milk and heavy cream, ensuring the mixture remains smooth before adding more liquid. Bring the sauce to a gentle simmer, stirring constantly, until it thickens enough to coat the back of a spoon (about 5-7 minutes).
  4. Season: Remove the pan from the heat. Stir in the salt, pepper, grated nutmeg, and the grated cheese (if using). Taste and adjust seasoning—it should be slightly salty now.
  5. Layer the Potatoes: Lay approximately 1/3 of the potato slices in the prepared dish, slightly overlapping, creating an even layer. Pour about 1/3 of the cream sauce evenly over the potato layer. Sprinkle with a little thyme (if using). Repeat this layering process two more times (potatoes, then sauce/thyme). The top layer should be the remaining sauce completely covering the potatoes.
  6. Bake Covered: Cover the baking dish tightly with aluminium foil. Bake for 50 minutes at 350°F (175°C).
  7. Brown the Top: Remove the foil and increase the oven temperature to 400°F (200°C). Bake uncovered for an additional 25-30 minutes, until the top is golden brown and bubbling, and the potatoes are completely tender when pierced.
  8. Rest: Remove the dish from the oven and let the scalloped potatoes rest uncovered for 15 minutes before serving. This allows the sauce to set and ensures clean slices.