This is a classic dish adapted from the Best Make Ahead Recipes cookbook – one of my favorite books. It’s perfect for dinner parties because you can pop the pre-prepared dish in the oven 20 minutes before serving. Frozen chopped spinach works well, but make sure to squeeze out as much of the water as possible. I usually put it in a fine mesh strainer and press it firmly with a wooden spoon; then press it between layers of paper towel to remove most of the moisture (otherwise it waters down the sauce).
2 tablespoons unsalted butter
1 medium shallot, minced (about 3 tablespoons)
2 teaspoons minced fresh thyme leaves
1 small garlic clove, minced or pressed through a garlic press (about 1/2 teaspoon)
2 cups heavy cream
4 teaspoons cornstarch
Salt and ground black pepper
2 (10-ounce) packages frozen spinach, thawed and squeezed dry
1 teaspoon minced fresh dill
1 ounce Parmesan cheese, grated (1/2 cup)
8 sole fillets, 1/4 to 1/2 inch thick
15 Ritz crackers, crushed fine (3/4 cup)
1 lemon, cut into wedges (for serving)
1. Melt 1 tablespoon of the butter in a medium saucepan over medium-high heat. Add the shallot and cook until softened, about 2 minutes. Stir in the thyme and garlic and cook until fragrant, about 30 seconds. Stir in 1 3/4 cups of the heavy cream and bring to a simmer. Whisk the remaining 1/4 cup heavy cream and cornstarch together, then stir into the saucepan. Continue to simmer until the sauce is thickened, about 2 minutes. Season with salt and pepper to taste. Set aside to cool.
2. Combine 1 cup of the sauce, spinach, dill, and Parmesan in a medium bowl and season with salt and pepper to taste. Pat the fish dry with paper towels and season with salt and pepper. Coat a 13 by 9-inch baking dish with the remaining 1 tablespoon butter.
3. Place the fish on a cutting board, smooth side down. Divide the spinach filling equally among the fish fillets, mounding it in the middle of each fillet. Fold the tapered end of the fish tightly over the filling and then fold the thicker end of the fish over the top to make a tidy bundle.
4. Arrange the fish bundles in the baking dish, seam side down (leaving space between each roll). Pour the remaining sauce evenly over the fish.
5. TO STORE: Cover tightly with plastic wrap and refrigerate for up to 24 hours.
6. TO SERVE: Adjust an oven rack to the middle position and heat the oven to 475 degrees. Sprinkle the fish with the Ritz cracker crumbs and bake until all but the very center of the fish turns from translucent to opaque and the filling is hot, about 20 minutes. Serve with the lemon wedges.