- 2garlic cloves, peeled, halved and crushed
- 2sprigs fresh thyme plus 1 tbsp fresh thyme leaves for garnish
- 2 1/2cups heavy cream
- 1/4tsp powdered nutmeg (optional)
- 3oz sliced Serrano ham
- 2medium sweet onions, peeled and quartered
- 6large russet potatoes, peeled
- 3cups shredded young Manchego cheese
- 1cup shredded Ibérico cheese
- 3tbsp olive oil and/or butter
- Sea salt and freshly ground black pepper
Assemble the gratin the day before you plan on serving it. This allows the starch from the potatoes to release into the cream for a thicker and creamier dish.
Combine the shredded cheeses and set aside. Pour the cream into a saucepan and add the garlic and thyme sprigs. Slowly warm over medium-low heat, until you see bubbles appearing around the edge of the pan and it is about to reach boiling point. Remove from the heat and transfer mixture to a 4-cup measuring jug or similar container. Stir in the nutmeg and leave to steep.
Stack ham slices and very loosely roll the stack lengthwise like a jelly roll. Slice the roll into ¼-inch slices and separate all the pieces. Add ½ tbsp of olive oil to a small sauté pan and fry the ham, stirring constantly over medium high heat until crispy. Remove to a plate lined with paper towels to absorb any excess oil.
Peel and slice the onions and potatoes about an 1/8 of an inch thick. (A mandolin or electric slicer produces the best results.) Submerge the potato slices into a bowl of cold, lightly salted water. Add the onions to the pan used for the ham and add 1 tbsp of olive oil. Sauté onions over medium heat until they just start to color.
With remaining olive oil or butter, grease the bottom and sides of a 13” paella pan or 9 x 12-inch baking dish. Arrange ¼ of the potato slices, slightly overlapping. Remove garlic and thyme sprigs from cream and pour ½ cup cream over potatoes. Use the back of a spoon to evenly distribute the cream. Sprinkle 1/3 of the sautéed onion, 1 cup shredded cheese, ¼ of the jamón Serrano, and season lightly with salt and pepper.
Repeat layering three more times, starting with the potatoes. Top final layer with remaining shredded cheese. Bake directly or cover pan with plastic wrap and refrigerate overnight.
Preheat oven to 375°F. If kept overnight, remove gratin from refrigerator and bring to room temperature. Remove plastic wrap and cover pan loosely with foil. Bake gratin 1 hour. Remove foil and bake until fork-tender, about 30 minutes more. Let potatoes rest 10 minutes before serving. Garnish with remaining jamón Serrano and fresh thyme leaves.
Serve warm as a tapa, side dish or with a crisp green salad for a lovely lunch.