Equipment
Ingredients
Vegetables
- 500 g yukon gold potatoes, peeled, unwashed to retain starch
- 500 g turnips, peeled
Cream Infusion
- 350 ml heavy cream, chilled
- 150 ml whole milk, chilled
- 3 garlic, crushed
- 4 fresh thyme, whole sprigs
- 30 g capers, drained and roughly chopped
- 8 g kosher salt
- 2 g black pepper, freshly cracked
- 1 g nutmeg, freshly grated
Crust
- 75 g hazelnuts, toasted, skinned, and roughly chopped
- 50 g parmesan cheese, finely grated
- 30 g unsalted butter, melted
Nutrition (per serving)
Method
Preheat your oven to 190C/375F. Lightly grease a baking dish with a small amount of butter or oil.
Using a mandoline slicer, carefully slice the potatoes and turnips to an even 3 millimeter thickness. Do not rinse the potato slices, as their natural starch is required to thicken the cream.
In a saucepan, combine the heavy cream, whole milk, crushed garlic, whole thyme sprigs, salt, black pepper, and grated nutmeg. Bring to a gentle simmer over medium heat, then immediately remove from heat. Let steep for 10 minutes.
Using a slotted spoon, remove and discard the garlic cloves and thyme sprigs from the cream mixture. Stir the chopped capers directly into the infused cream.
Arrange the potato and turnip slices in the prepared baking dish, alternating them in a shingled pattern. Pour the infused cream and caper mixture evenly over the top. Gently press down on the vegetables so the liquid rises up around them.
Cover the baking dish tightly with aluminum foil. Bake at 190C/375F for 45 minutes until the vegetables offer very little resistance when pierced with a paring knife.
While the gratin bakes, combine the chopped hazelnuts, grated Parmesan cheese, and melted butter in a small mixing bowl. Toss until the nuts and cheese are evenly coated.
Remove the baking dish from the oven and carefully remove the foil. Scatter the hazelnut-Parmesan mixture evenly over the top of the gratin.
Return the gratin to the oven, uncovered. Bake for an additional 20 minutes until the cream is bubbling vigorously around the edges and the crust is deep golden brown and crispy.
Remove the gratin from the oven and allow it to rest at room temperature for 10 to 15 minutes before serving. This resting period is critical for the cream to set up and bind the layers.
Chef's Notes
- Retaining the potato starch by not rinsing the slices is the secret to a naturally thickened, luxurious sauce without the need for a flour roux.
- The earthy bitterness of turnips pairs brilliantly with rich dairy, but utilizing younger, smaller turnips ensures a sweeter flavor profile with less woody texture.
- Capers add tiny bursts of acidity and brine that cut through the richness of the cream and cheese. Be sure to drain them well so their preserving liquid does not curdle the hot milk.
- Using a mandoline is not just for aesthetics; uniform slices ensure everything cooks at the exact same rate. Inconsistent knife cuts are the leading cause of failed gratins.
Storage
Refrigerator: 3 days — Store tightly covered. The crust will lose its crunch after chilling.
Reheating: Reheat in a 175C/350F oven uncovered for 20 minutes until bubbling and crust is recrisped.
