Qarch ba Kerm (قارچ با کرم) — Creamy Mushroom Gratin

• 500 gCremini mushrooms (or white button mushrooms), cleaned and sliced 6 mm (Wipe with a damp towel; avoid soaking in water)
• 45 gUnsalted butter (Divided: 30 g for sautéing, 15 g for sauce)
• 12 gGarlic, finely grated or minced (About 3 large cloves)
• 5 gFine sea salt (About 1 tsp; adjust after reducing)
• 2 gFreshly cracked black pepper (About 1 tsp)
• 240 mlHeavy cream (35% fat) (Room temperature for easier tempering)
• 2 largeEgg yolks (About 34 g total; for thickening and silkiness)
• 80 gGrated Gruyère (or low-moisture mozzarella) (Gruyère gives deeper nuttiness; mozzarella melts milder)
• 12 gFlat-leaf parsley, finely chopped (About 1/2 cup loosely packed)

Instructions

1. 1

   Heat oven to 230°C (450°F) with a rack in the upper third. Pat mushrooms completely dry, then slice to 6 mm so they cook evenly. Set out cream to warm slightly at room temperature. This prevents the sauce from splitting when it meets the hot pan and helps the yolks temper smoothly.

2. 2

   In a wide skillet over medium-high heat, melt 30 g butter until foamy (about 45 seconds). Add mushrooms in a single layer and cook 6–8 minutes, stirring only occasionally, until they release liquid and that liquid fully evaporates. Browning at the end is key for deep umami and a non-watery gratin.

3. 3

   Lower heat to medium. Add garlic and cook 30–45 seconds until fragrant, not browned. Stir in sea salt and black pepper, then cook 1 minute more. Transfer mushrooms to a 20 cm (8-inch) baking dish, spreading them evenly so the sauce later coats every slice and bakes into a uniform layer.

4. 4

   Return the skillet to medium heat and melt the remaining 15 g butter. Pour in the heavy cream and bring to a gentle simmer (not a boil) for 3–4 minutes, stirring, until slightly thickened and able to lightly coat a spoon. Remove from heat and let stand 60 seconds to cool slightly before adding yolks.

5. 5

   In a bowl, whisk egg yolks for 10 seconds. Slowly whisk in 60 ml of the hot cream mixture to temper. Then pour the tempered yolks back into the skillet, whisking constantly. Return to low heat and cook 1–2 minutes, stirring continuously, until the sauce turns glossy and thickens to a nappé consistency; do not exceed 75°C to avoid curdling.

6. 6

   Pour the warm cream-yolk sauce over the mushrooms and gently fold to coat without breaking the slices. Sprinkle grated Gruyère (or mozzarella) evenly across the top. Bake 8–10 minutes at 230°C until bubbling at the edges, then broil 1–2 minutes for a golden crust; watch closely to prevent scorching.

7. 7

   Rest the dish 5 minutes so the sauce sets and stays velvety when served. Sprinkle chopped flat-leaf parsley over the top for freshness and color. Serve hot or warm, scooping from the edges where the sauce caramelizes slightly and the mushrooms are most concentrated in flavor.