1 medium celeriac
2 medium parsnips
2 medium baking potatoes
1 3/4 c broth
1 c whole milk
1 t salt (omit if broth is salted)
1 clove garlic, halved
1 T olive oil, plus extra for greasing baking pan
1 T flour
(salt and) pepper
1/2 c grated Gruyère cheese; or Emmental; Jarlsberg; Swiss (or whatever’s on hand)
1. Quarter celeriac. Peel. Trim (and peel) parsnips and potato. Cut vegetables into 3/4-inch pieces. Combine in saucepan with broth, milk, and salt. Bring to a simmer and simmer gently until barely tender, about 10 minutes.
2. Preheat oven to 375ºF. Move an oven rack to the center of the oven. Rub a shallow 1-1/2 quart baking dish with garlic halves. Brush dish with some oil. Drain vegetables in a colander, reserving cooking liquid. Transfer vegetables to the baking dish.
3. Heat oil in the saucepan. Add flour and stir for a minute or two, until the flour is toasty. Gradually whisk in 1-1/2 cups of the reserved cooking liquid. Boil a minute or two, stirring constantly, until thickened some. Taste for seasoning. Pour this over vegetables. Sprinkle grated cheese over.
4. Bake until lightly browned and bubbling, about 1/2 hour.