Big-batch Creamy Seafood Casserole

Divide cup of the oil between 2 large pots and heat over medium heat. Divide the onions, carrots, parsnips, and celery between the pots and cook, stirring occasionally, until tender, 18 to 20 minutes. Dividing evenly, sprinkle with the flour and cook, stirring, for 1 minute (do not let darken). Divide the wine between the pots and simmer for 1 minute.Divide the cream between the pots; season each with 1 teaspoon salt and teaspoon pepper and bring to a boil.

Remove from heat and, dividing evenly, stir in the parsley. Divide the vegetable mixture among four 8-inch square baking dishes and let cool.Meanwhile, place the potatoes in a large pot and add enough cold water to cover. Bring to a boil and add 1 tablespoon salt. Reduce heat and simmer until tender, 15 to 18 minutes. Reserve 3 cups of the cooking water, drain the potatoes, and return them to the pot.

Bake the casserole on a rimmed baking sheet at 375 F until golden brown, 20 to 25 minutes.To freeze and cook later: Freeze the unbaked casserole, tightly sealed, for up to 3 months. To cook, thaw the casserole and bake, uncovered, on a rimmed baking sheet at 375 F until heated through and golden brown, 40 to 45 minutes.