Potato and Gruyere Oven Gratin
Thin potato slices baked in a seasoned cream and egg custard under a golden gruyere crust. A comforting French-style side dish with a bubbling, browned top.
- Total
- 88 min
- Prep 20 · Cook 58 · Rest 10
- Serves
- 1
- Difficulty
- Easy
You'll practice: Seasoning in layers · Whisking
- Savory
- French
- Oven
Instructions
-
Heat the oven to 180°C. Peel the potatoes and slice them 3 mm thick with a mandoline or sharp knife. Peel the onion and slice it thinly.
~15 min
Uniform 3 mm slices cook at the same rate, so the potatoes and custard finish together.
Slice the potatoes no thicker than 3 mm; thicker slices stay firm while the custard overcooks.
-
In a mixing bowl, whisk the 2 eggs with 200 ml cream, 100 ml water, 1 tsp salt and 0.5 tsp black pepper until smooth.
~3 min
Whisking the eggs into the cream disperses them evenly, so the custard sets smooth rather than curdled.
Seasoning in layers Season the custard and distribute it evenly over the layered potatoes. Taste the raw custard; it should be slightly saltier than you want the finished dish, since the potatoes absorb salt.
Whisking Whisk the eggs and cream until completely homogeneous, with no streaks of yolk or white. Stop before the mixture becomes frothy, which can create bubbles that mar the custard's surface.
-
Spread half the potato slices in the baking dish, scatter over the sliced onion, then add the remaining potatoes in an even layer. Pour the 200 ml cream mixture over the top and press the potatoes down so they sit in the liquid.
~5 min
Pressing the potatoes into the liquid ensures the custard surrounds every slice and no dry pockets remain.
Seasoning in layers Season the custard and distribute it evenly over the layered potatoes. Taste the raw custard; it should be slightly saltier than you want the finished dish, since the potatoes absorb salt.
-
Cover the dish tightly with foil and bake for 35 minutes, until the potatoes are nearly tender when pierced with a knife.
~35 min
Foil traps steam, which cooks the potatoes through before the custard dries out or the top browns.
-
Remove the foil and scatter the 120 g grated gruyere evenly over the top. Bake uncovered for 20 minutes, until the cheese is melted and golden brown and the potatoes are fully tender.
~20 min
Uncovering lets the cheese melt and brown while the exposed custard sets and the potatoes finish tender.
If the top browns faster than the potatoes soften, lay a piece of foil loosely over the dish for the last few minutes.
-
Let the gratin rest for 10 minutes so the custard sets, then cut into portions and serve.
~10 min
Resting allows the just-set custard to firm up so portions cut cleanly instead of running.