I have about an hour of oven time while the turkey is resting. Using stock and cream for the liquid.
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Amanda is the Design & Home Editor at Food52
I don't think parboiling is necessary (especially since your vegetables are sliced thinly in a gratin). Just follow the recipe but bake the dish a little longer than stated, 5 to 10 minutes to start—and if the top gets dark, just cover and keep it in there until bubbly throughout!