Sally Pasley Vargas for The Boston Globe

Serves 4

Butter (for the dish)
3 slices country bread, made into bread crumbs
(1½ cups)
2 tablespoons olive oil
1 tablespoon chopped parsley
2 onions, thinly sliced
Salt and pepper, to taste
4 teaspoons flour
2 cups leftover meat broth
2 cups cooked celery root, carrots, and rutabaga, cut into matchsticks
2 cooked beef shanks, meat cut into slices

1. Set the oven at 450 degrees. Lightly butter a 2-quart shallow baking dish.

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2. In a small bowl, toss the bread crumbs, 1 tablespoon of the olive oil, and parsley together.

3. In a large skillet over medium-high heat, heat the remaining
1 tablespoon olive oil. Add the
onions, salt, and pepper. Cook,
stirring often, for 8 minutes or until they are lightly browned. Stir in
the flour and cook, stirring, for 2 minutes. Stir in the broth a little at a time. Bring to a simmer. Stir in the leftover vegetables. Taste for seasoning and add more salt and pepper, if you like.

4. Transfer half the onions and
vegetables to the baking dish. Add
a layer of sliced beef. Cover with the remaining vegetables. Spread the bread crumbs on top.

5. Bake the gratin for 20 minutes or until the bread crumbs are browned and the gratin is hot.

Sally Pasley Vargas