- Blanch the spinach in boiling water until wilted, then squeeze dry. You should have about ¾ pound (350g) blanched spinach.
- Melt the ¼ cup butter in a pan, add the picked marjoram leaves and cook for a minute. Add the spinach and stir to combine the flavors. Season, then leave to cool. When cooled, chop roughly.
- In a large bowl, lightly beat the ricotta with a fork. Sift in the flour. Add the egg yolks, nutmeg and Parmesan and mix well. Finally, fold in the cooled spinach mixture until well combined. Taste for seasoning.
- Line a baking sheet with parchment paper.
- Use two dessert spoons for shaping the gnocchi: with one of them take a small spoonful of the mixture and, using the other spoon, mold the mixture so that it forms a gnoccho (a small oval dumpling about ¾ inch [2cm] in diameter). Place on the baking sheet. Continue making the gnocchi—they should all be the same size.
- To make the sage butter, heat the 1 cup butter gently so it separates. Pour out the clarified butter into a clean pan and return to the heat. When very hot, add the sage leaves. Remove from the heat and allow to cool.
- Bring a large pot of salted water to the boil, then lower the heat to a simmer. Gently place the gnocchi in the water in batches—it is important not to overcrowd the pot. When the gnocchi come back to the surface, remove carefully with a slotted spoon and briefly place the spoon on paper towels to drain off excess water.
- Keep the gnocchi warm, tossed with some of the sage butter, in a warm oven while you cook the rest.
- Serve immediately on warm plates with the remaining sage butter and extra Parmesan.
Excerpted from River Café London: Thirty Years of Recipes and the Story of a Much-Loved Restaurant by Ruth Rogers, Rose Gray, Sian Wyn Owen and Joseph Trivelli. Copyright © Ruth Rogers and Rose Gray 1995. Published in the United States by Borzoi Books an imprint of Alfred A. Knopf, a division of Penguin Random House LLC, New York. Reproduced by arrangement with the Publisher. All rights reserved.