010 / 75 · Crisp-Topped and Potato Comfort

Mushroom and Leek Potato-Rösti Bake

One 9-in/23-cm square baking dish of at least 3 qt/2.8 L; 4 main-dish portions · Active 40 min · Total 1 hr 45 min

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A thin rösti-style potato layer covers browned mushrooms and soft leeks in a lightly set sour-cream filling. There are no frozen breakfast potatoes in this version: freshly grated waxy potatoes are squeezed, loosened and spread in a shallow layer. The mushrooms supply browned flavor and the leeks a softer sweetness beneath the crisp strands.

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Illustrated mushroom and leek bake with a thin crisp shredded-potato roof.

Wash the leek where the dirt hides

Split the white and pale-green leek lengthwise, then fan the layers under running water before slicing. Soil trapped between the layers should not end up in the filling. Weigh after trimming and washing, and let the slices drain well. Cook them gently until soft rather than trying to brown the thin edges. Their job is to form a tender background for the mushrooms. Tough dark-green leaves belong in a different preparation, not hidden under this topping.

Mushrooms need two batches

A crowded pan lets released water collect faster than it can evaporate. Brown half the mushrooms at a time over a lively heat, then reunite them with the softened leeks. Keep cooking until the mixture is moist but no longer sitting in liquid. Let it cool briefly before folding it into beaten eggs and dairy, so the egg does not set in streaks on contact. The oven then makes a gentle binding layer rather than a deep custard. It should hold a spoonful together without becoming a firm cheese pie.

Squeeze, loosen, scatter

Grate potatoes only when the filling is nearly ready. Squeeze hard in a clean towel, open the bundle and separate the strands with your fingers before adding oil. Pressing the squeezed mass straight onto the pan makes a dense slab. Scatter it instead, keeping the depth fairly even and leaving tiny high points. It is a rösti-style roof, not a promise that the entire pan will behave like a fried rösti pancake. The underside stays softer where it meets the filling; the top and edges provide the crunch.

Ingredients

  • 1 tablespoon butter (15 g)
  • 1 large leek, white and pale-green parts washed and sliced (200 g prepared)
  • 1 lb 2 oz mushrooms, sliced (500 g)
  • 3 tablespoons neutral oil (45 ml), divided: 1 tablespoon/15 ml for mushrooms and 2 tablespoons/30 ml for potatoes
  • 1 garlic clove, finely chopped (3 g)
  • 1 teaspoon dried thyme
  • 2 large eggs
  • 1/2 cup sour cream (120 g)
  • 1/2 cup milk (120 ml)
  • 1 lb 9 oz waxy potatoes, scrubbed and coarsely grated (700 g prepared)
  • 1/2 teaspoon fine salt (3 g), divided equally between filling and potatoes
  • 1/4 teaspoon black pepper

Set out

Oven, 9-in/23-cm square baking dish, at least 3 qt/2.8 L, 12-in/30-cm skillet, Coarse grater, Clean towel, Two mixing bowls, Whisk, Food thermometer, Rimmed baking sheet, Suitable foil if the topping colors before the center finishes

Allergens

Egg, Milk. Check labels and substitutions.

Make it

  1. Heat the oven to 425°F (220°C). Put the dish on a rimmed sheet. Melt butter in the skillet over medium-low heat and cook leek 8–10 minutes until soft. Transfer to a bowl.
  2. Add 7.5 ml oil and half the mushrooms to the skillet. Cook over medium-high heat for 7–9 minutes until browned and their water has evaporated. Transfer to the leek bowl. Repeat with the remaining mushrooms and 7.5 ml oil. Return all vegetables to the skillet, add garlic and thyme and stir 30 seconds. Take off the heat and cool for 10 minutes.
  3. Beat eggs, sour cream, milk, half the salt and pepper in the second bowl. Fold in the warm, not hot, mushroom mixture and spread in the dish.
  4. Grate potatoes and squeeze firmly in the clean towel. Loosen the strands in a bowl, toss with remaining 30 ml oil and remaining salt, then scatter over the filling in an even layer about 1/2 in/1 cm thick. Do not compress.
  5. Bake 35–45 minutes until the potato is cooked through, the top is golden and the filling reaches 165°F (74°C) in the center and several other spots. Shield any over-browning area loosely with foil while the center finishes. Rest 5 minutes before serving.

Grate at the right moment

Brown the mushrooms before starting the potatoes. This keeps the raw shreds from sitting around while a long pan stage still needs attention, and gives you a clear counter for squeezing them.

A useful detail

The 105-minute total allows two mushroom batches and their cooling stage. The topping is shallow; do not use a small deep round pot. A golden surface alone does not confirm the egg-and-dairy filling is set.

Another way

  • Use 500 g mixed cultivated mushrooms in place of the standard mushrooms, keeping two batches and the full evaporation stage. Do not add uncooked mushrooms after making the dairy mixture.

Keep it well

Refrigerate shallow portions within 2 hours, or 1 hour above 90°F (32°C), at 40°F (4°C) or below. Use within 2 days or an earlier dairy deadline. Reheat to 165°F (74°C). Refrigeration is preferable to freezing this egg-and-sour-cream filling; the potato surface also softens after storage.