Set aside 5 cups packed spinach leaves. Fill a large pot with 1 in. water and fit with a steamer basket. Cover and bring to a boil. Add remaining spinach, reduce heat to a simmer, and steam, stirring once, until wilted, 2 to 3 minutes. Drain and rinse with cold water. Wrap spinach in a clean kitchen towel and squeeze out excess moisture. Finely chop; you should have about 1/2 cup.
Whisk egg in a large bowl to blend, then stir in cooked spinach, ricotta, 1 cup parmesan, the salt, and nutmeg. Gradually stir in 1 2/3 cups flour, mixing thoroughly until dough comes away from side of bowl (it will be soft).
Turn dough out onto a well-floured work surface and gather into a ball, sprinkling with more flour as needed so surface is dry. Reflour board. Cut dough into 8 pieces. On a work surface, roll each piece with your fingers, starting from the center, into an even 12-in. rope, then cut or snip each rope into 3/4-in. pieces. Line 2 rimmed baking sheets with parchment paper and sprinkle with flour.
Hold a fork, tines facing down, on a work surface. Dip fingers of your other hand in flour, set one of the gnocchi on the tines with uncut edges to the sides, and press lightly to make indentations. Roll off to bottom of fork; set on prepared baking sheet. Repeat to shape remaining gnocchi.
Bring a large pot of salted water to a boil. Meanwhile, heat butter in a large nonstick frying pan over medium heat until light brown, 3 to 4 minutes. Add pine nuts and cook, stirring often, until golden, about 1 minute. Stir in lemon zest, then pour into a small bowl. Set pan aside.
Working in 2 batches, boil gnocchi until they rise to the surface, 3 to 4 minutes. With a slotted spoon, transfer to a rimmed baking sheet.
Spoon 1 tbsp. brown butter from bowl of pine nuts back into frying pan. Over medium heat, brown half of gnocchi, turning once, 3 to 4 minutes per side. Transfer to a warm shallow serving bowl. Repeat with another 1 tbsp. brown butter and remaining gnocchi.
Add remaining butter mixture, reserved 5 cups spinach leaves, and the broth to pan and cook, tossing, until spinach wilts, about 1 minute. Pour over gnocchi and toss to coat. Top with about 1/2 cup more parmesan.
Make ahead: Through step 4, up to 6 weeks, frozen; freeze on baking sheets, then transfer to an airtight container or bag. Boil frozen (3 to 4 minutes, same as fresh).