Root Vegetable Gratin
This gratin relies on the natural starches of the vegetables to bind the cream. Use a mandoline for precision, as even thickness ensures everything cooks through simultaneously.
Uniformity is the only requirement for success.
If your slices vary in thickness, the dish will be unevenly cooked—some parts mushy, others raw. Take your time with the slicer.
- Mandoline slicer
- 9x13 inch ceramic baking dish
- Large heavy-bottomed saucepan
- Whisk
What goes in.
- 1 lbYukon Gold potatoes, peeled
- 1 lbparsnips, peeled
- 1/2 lbceleriac, peeled
- 2 cupsheavy cream
- 3 clovesgarlic, smashed
- 4 sprigsfresh thyme
- 1 tspkosher salt
- 1/2 tspblack pepper, freshly cracked
- 1/2 cupGruyère cheese, grated
Steeping the aromatics
Heat the cream with the garlic and thyme until it just reaches a simmer, then remove from heat and let it sit for ten minutes; this extracts the flavor without scorching the dairy.
The method.
Prep the cream
Bring cream, garlic, and thyme to a bare simmer in a saucepan. Turn off the heat and let steep.
Slice the vegetables
Using the mandoline, slice potatoes, parsnips, and celeriac to 1/8-inch thickness. Toss them in a large bowl with the salt and pepper.
Layer
Strain the cream, discarding the garlic and thyme. Arrange the vegetable slices in overlapping shingles in the baking dish, pouring a small splash of cream between every two layers.
Bake
Pour the remaining cream over the top. Cover with foil and bake at 375°F for 40 minutes. Remove the foil, sprinkle with Gruyère, and bake uncovered for another 25 minutes until the top is deeply browned and the vegetables yield to a knife.
Other turns to take.
Earthy Twist
Replace the celeriac with thinly sliced sweet potato for a slight sweetness that cuts through the rich cream.
Herb-Forward
Add one tablespoon of finely minced fresh rosemary to the cream while it steeps.
When it doesn't go to plan.
Do not rinse the vegetables after slicing; the starch on the surface is necessary to thicken the cream sauce.
If the top browns too quickly before the center is tender, tent a piece of foil loosely over the dish.
Let the gratin stand for at least 15 minutes after pulling it from the oven; it needs that time to set properly.
The ones that keep coming up.
Can I make this ahead of time?
You can assemble the dish and keep it covered in the refrigerator for up to 4 hours before baking. Add 10 minutes to the initial covered bake time.
Why is my sauce watery?
Likely because the dish was sliced too thick or not cooked long enough to reduce the cream. Ensure the vegetables are paper-thin.
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