Equipment
* optional
Ingredients
Vegetables
- 600 g potatoes, peeled and sliced 3mm thick
- 2 fennel bulbs, trimmed, cored, and thinly sliced
- 1 yellow onion, thinly sliced
- 2 garlic, minced
Dairy & Seasoning
- 30 g unsalted butter, divided
- 300 ml heavy cream, 35% fat or higher
- 150 ml whole milk
- 100 g gruyère cheese, grated
- 30 g parmesan cheese, finely grated
- 5 g fresh thyme leaves, picked
- 1 g nutmeg, freshly grated
- 8 g kosher salt
- 2 g white pepper, ground
Nutrition (per serving)
Method
Preheat your oven to 190°C (375°F). Grease the baking dish generously with 10g of butter.
In a large skillet, melt the remaining 20g butter over medium heat. Add sliced onions and fennel. Sauté for 10-12 minutes until soft and slightly translucent, but not heavily browned.
In a mixing bowl or jug, whisk together heavy cream, milk, minced garlic, thyme, nutmeg, salt, and white pepper.
Arrange half of the sliced potatoes in the baking dish. Top with the sautéed fennel and onion mixture, then half of the Gruyère cheese. Layer the remaining potatoes on top. Pour the cream mixture evenly over the entire dish.
Press the potatoes down gently to ensure they are submerged in the liquid. Sprinkle the remaining Gruyère and Parmesan cheese over the top.
Cover tightly with foil and bake for 40 minutes. Remove foil and bake for another 20-30 minutes until the top is deep golden brown and the potatoes are tender when pierced with a knife.
Remove from oven and let the gratin rest for at least 15 minutes before serving. This allows the sauce to thicken and the layers to set.
Chef's Notes
- Sweating the fennel before assembling is critical; raw fennel releases too much water during baking and can result in a soupy gratin.
- Do not rinse the potato slices after cutting. The surface starch helps thicken the cream sauce as it bakes.
- If using a mandoline, always use the safety guard to protect your fingers.
- For a deeper anise flavor, add a splash of Pernod or Sambuca to the fennel while sautéing.
Storage
Refrigerator: 3 days — Cover tightly with foil or transfer to an airtight container.
Freezer: 1 month — Texture of potatoes may become slightly grainy upon thawing; bake from frozen covered.
Reheating: Reheat in a 175°C (350°F) oven covered with foil for 20 minutes to prevent the emulsion from breaking.
