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Spinach Au Gratin with Sautéed Mushrooms

A masterclass in moisture extraction and roux-based dairy emulsions. By aggressively draining blanched spinach to protect the structure of a rich, Gruyere-laced béchamel sauce, this decadent gratin is crowned with sherry-glazed, deeply caramelized mushrooms for a flawless textural contrast.
Print Recipe
Prep Time 15 minutes
Cook Time 30 minutes
Total Time 45 minutes
Servings: 4 servings
Course: Side Dish
Ingredients Method

Ingredients
  

The Harvest Foundation & Moisture Control
  • 1 20-ounce package frozen chopped spinach, thawed (or 2 pounds fresh spinach, steamed)
The Sherry-Glazed Mushrooms
  • 2 tablespoons olive oil
  • 2 tablespoons unsalted butter
  • 8 ounces fresh mushrooms cremini or button, thickly sliced (about 2 ½ cups)
  • ¼ cup dry sherry for deglazing
  • 1 teaspoon kosher salt
  • ½ teaspoon coarse black pepper
The Gruyere Béchamel (Mornay Sauce)
  • 3 tablespoons unsalted butter divided: 2 for roux, 1 for topping
  • 2 tablespoons unbleached all-purpose flour
  • 1 ½ cups whole milk
  • ¼ teaspoon ground nutmeg
  • 4 ounces Gruyere cheese freshly grated (about ½ cup)
The Structural Crust
  • 2 ounces Parmesan cheese freshly grated (about ¼ cup)
  • Paprika for dusting

Method
 

Moisture Extraction (The Spinach)
  1. If using frozen spinach, thaw completely. If using fresh, steam 2 pounds of spinach until fully wilted.
  2. Place the cooked spinach into a fine-mesh colander. Using your hands or heavy paper towels, aggressively press and squeeze out as much moisture as physically possible. (This critical architectural step prevents the residual water from breaking the rich cheese sauce during the bake). Transfer the dry spinach to a large mixing bowl and set aside.
The Mushroom Sear & Deglaze
  1. Heat the 2 tablespoons of olive oil and 2 tablespoons of butter in a large skillet over medium-high heat until foaming.
  2. Add the sliced mushrooms in a single, even layer. Do not stir immediately; allow them to sear undisturbed until deeply golden brown on the bottom, about 4 to 5 minutes.
  3. Toss the mushrooms to brown the second side for 2 minutes.
  4. Reduce the heat to medium and pour in the dry sherry to deglaze the pan, scraping up the caramelized fond. Cook until the liquid completely evaporates, about 3 minutes. Season with kosher salt and black pepper, then remove from heat.
The Gruyere Béchamel Emulsion
  1. Preheat the oven to 375°F.
  2. In a medium saucepan, melt 2 tablespoons of butter over medium heat. Whisk in the flour continuously for 1 minute to cook out the raw starch and establish a pale roux.
  3. Slowly stream in the whole milk, whisking constantly until the sauce is completely smooth and begins to bubble and thicken, about 5 minutes.
  4. Remove from heat. Whisk in the ground nutmeg and the freshly grated Gruyere cheese until completely melted into a glossy, thick sauce.
The Architectural Assembly & Bake
  1. Pour the hot Gruyere sauce directly over the dry, squeezed spinach in the mixing bowl. Stir vigorously until the spinach is thoroughly coated and suspended in the cheese sauce.
  2. Transfer the creamed spinach mixture into a shallow ceramic au gratin dish (or individual ramekins).
  3. Layer the sherry-glazed mushrooms evenly over the top of the spinach.
  4. Scatter the grated Parmesan cheese heavily across the mushrooms. Dot the surface with the remaining 1 tablespoon of butter (cut into tiny pieces) and finish with a light dusting of paprika.
  5. Bake in the preheated 375°F oven for 10 to 12 minutes, until the casserole is bubbling violently at the edges and the Parmesan crust is deeply golden brown. Serve immediately.