Mushroom Matzo Kugel

Preparation

1. stock

   Step 1

   Heat broiler. Place onion on a small baking sheet and broil, turning halfway through, until charred, about 5 minutes per side. Transfer to a small saucepan and add parsley, all mushrooms, peppercorns, and 5 cups water. Bring to a boil, then reduce heat and cook at a bare simmer until broth is reduced to 3½ cups and is very cloudy, about 1½ hours. Strain stock through a fine-mesh sieve into a large heatproof measuring glass or an airtight container (you should have about 3 cups); discard solids. Stir in salt.

   Do ahead: Broth can be made 3 days ahead. Let cool; cover and chill.

2. Kugel

   Step 2

   Preheat oven to 300°. Butter a 13x9" baking dish. Break matzo into 3" pieces; place in a large bowl. Pour 2 cups stock over and gently toss to coat; set remaining 1 cup stock aside. Let sit until matzo is soaked and breakable but still holds its shape, about 30 minutes.

   Step 3

   Meanwhile, whisk eggs, crème fraîche, and cream in a medium bowl to combine; season with salt.

   Step 4

   Remove ribs and stems from Swiss chard leaves. Finely chop ribs and stems, then coarsely chop leaves. Heat 4 Tbsp. butter in a large skillet over medium-high. As soon as butter is foaming, add shiitake and maitake mushrooms and cook, stirring, until liquid is released and mushrooms are reduced by half in size, about 5 minutes. Season with salt and transfer to a medium bowl.

   Step 5

   Reduce heat to medium. Heat remaining 4 Tbsp. butter in same skillet. Add onion and a pinch of salt and cook, stirring occasionally, until translucent, about 5 minutes. Add Swiss chard ribs and stems, increase heat to medium-high, and cook, stirring, until onion is golden brown and ribs and stems are softened, about 5 minutes. Add Swiss chard leaves in 2 batches, letting wilt slightly between additions, and cook, stirring, until completely wilted and no longer wet-looking, about 4 minutes. Season with salt. Scrape into bowl with mushrooms and let cool 10 minutes.

   Step 6

   Add mushroom mixture to bowl with matzo. Season with salt, then stir in egg mixture. If kugel looks dry, add more reserved stock ¼ cup at a time until moist but not watery. Carefully pour into prepared dish; bake until top is golden brown and kugel is set, 55–65 minutes. Let cool slightly before serving.