Creamed spinach sauce – 2 1/2 tablespoons sunflower oil – 2 tablespoons all-purpose flour – 1 pound (450 g) frozen spinach, thawed – 1 large egg, whisked – 1 teaspoon garlic powder, more to taste – 3/4 cup (180 g) sour cream – 1 cup (240 ml) whole milk – 1 teaspoon fine sea salt, more to taste Béchamel sauce – 2 tablespoons (30 g) unsalted butter – 2 tablespoons (20 g) all-purpose flour – 1 1/4 cups (300 ml) warm milk – 1/4 teaspoon ground nutmeg – 1/2 teaspoon salt – few grinds of black pepper For lasagna – 20 uncooked lasagna sheets, 400 g or 14 oz – 10.5 oz (300 g) aged (low moisture) mozzarella cheese, grated – 1 tablespoon fresh chopped parsley