In a large bowl, mix the chopped spinach, ricotta cheese, flour, egg, salt, and nutmeg. Stir until the ingredients are well combined, creating a soft but slightly sticky dough. If necessary, add more flour a tablespoon at a time until the dough is workable.
Dust a clean surface with flour. Divide the dough into four equal portions. Roll each portion into a long rope about ½ inch thick. Cut the ropes into 1-inch pieces, then use a fork to create ridges on each piece, if desired.
In a large pot of boiling salted water, carefully drop in the gnocchi in batches. Cook until they float to the surface, about 2-3 minutes. Use a slotted spoon to remove the cooked gnocchi and transfer them to a plate.
In a large skillet over medium heat, add the olive oil and minced garlic. Sauté until the garlic is fragrant, about 30 seconds. Pour in the heavy cream and simmer for 2-3 minutes. Stir in the grated Parmesan cheese until melted and smooth. Season with salt and freshly ground black pepper to taste.
Add the cooked gnocchi to the skillet with the cream sauce. Gently toss to coat the gnocchi evenly in the sauce, warming everything through for an additional 2 minutes.
Plate the creamy spinach ricotta gnocchi and garnish with fresh basil leaves and a sprinkle of extra Parmesan cheese, if desired.