Sheet-Pan Spinach Lasagna
Step 1
Place a rack in middle of oven; preheat to 375°. Heat 1 Tbsp. extra-virgin olive oil in a large skillet over medium-high. Cook 1 lb. hot Italian sausage, casings removed, 1 medium onion, finely chopped, and 2 garlic cloves, finely chopped, breaking up sausage into small pieces with a wooden spoon and stirring occasionally, until onion is softened and translucent and sausage is cooked through, 8–10 minutes. Remove from heat and let cool slightly. Break up any remaining large pieces of sausage with a fork or potato masher.
Step 2
Meanwhile, place one 1-lb. bag frozen spinach in a blender. Heat 3 cups whole milk, 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, ½ tsp. freshly ground pepper, 1 lemon, zest removed in wide strips with a vegetable peeler, and remaining 4 whole garlic cloves in a medium saucepan over medium-high, stirring occasionally, just until milk is steaming, about 5 minutes. Immediately pour over spinach and blend, starting on low speed and gradually increasing to high, until mixture is smooth and bright green.
Step 3
Toss 8 oz. low-moisture mozzarella, coarsely grated (about 2 cups), and 8 oz. Parmesan, finely grated (about 4 cups), in a large bowl to combine; set aside 1½ cups for topping. Add remaining cheese mixture to spinach sauce in blender. Pour in 1 cup heavy cream; blend just until combined.
Step 4
Pour one third of spinach sauce (about 2¼ cups) onto an 18×13″ rimmed baking sheet and spread to edges of pan with a large spoon. If 1 lb. fresh lasagna sheets are in large strips, cut in half or thirds (this allows the noodles to become appealingly wavy in the oven). Arrange half of sheets in a single layer to cover sauce, trimming to fit as needed. Spoon sausage mixture evenly over pasta, then top with half of remaining sauce. Arrange remaining lasagna sheets in a single layer across surface. Pour remaining sauce over and spread evenly to cover pasta. Scatter reserved cheese mixture on top.
Step 5
Bake lasagna until top is golden brown in spots, filling is
set around edges, and a skewer or toothpick slides easily through center, 25–35 minutes.
Let sit 10 minutes before cutting into squares.
