How to Make It
In a large, deep skillet, melt the butter. Add the garlic, onion, bay leaf and red pepper and cook over moderate heat until the garlic is fragrant. Add the tomatoes and their juices and bring to a boil. Simmer the sauce over low heat, stirring occasionally, until thickened and reduced to 2 1/2 cups, about 1 1/2 hours. Discard the garlic, onion and bay leaf. Season the sauce with salt and keep warm.
Meanwhile, heat a medium skillet. Add the spinach, a handful at a time, and stir over moderately high heat until wilted; transfer to a colander; let cool slightly. Squeeze the spinach dry and finely chop it.
Bring a large pot of salted water to a boil. In a food processor, combine the spinach with the ricotta, eggs, nutmeg, and the 1/4 cup of Parmesan and process until blended. Add the flour in 3 batches, pulsing between additions, until almost incorporated. Scrape the gnudi dough onto a lightly floured work surface and knead 5 to 10 times, until smooth.
Add one-fourth of the gnudi dough to a large, resealable plastic bag; with scissors, cut a 1/2-inch corner from the bag. Working over the boiling water, squeeze the dough through the corner opening and use a knife to cut it into 1-inch pieces. Cook the gnudi over moderately high heat until firm, about 3 minutes. With a slotted spoon or wire skimmer, transfer the gnudi to a baking sheet. Repeat with the remaining dough.
Carefully transfer the gnudi to the tomato sauce and stir lightly to heat through. Spoon into shallow bowls and serve at once, passing more Parmesan at the table.