Yes, you read the title of the recipe correctly. I make gnocchi with ricotta cheese, not potatoes as you might expect. My grandmother taught me how to make them this way, and though they are less forgiving than potato gnocchi, I love their soft, delicate texture and flavor. They practically melt in your mouth. It's crucial to find high-quality ricotta cheese from a good Italian market, cheese shop, or gourmet store and then drain it, and to handle the gnocchi gently. Because this is more about the gnocchi than the sauce, the sauce is exceedingly easy to make, but nevertheless very tasty.
To drain the ricotta cheese, wrap it in a double thickness of cheesecloth and suspend the cheesecloth ball over a bowl, or put the wrapped cheese in a fine-mesh sieve or chinois rested on the rim of a bowl. Refrigerate overnight to give the whey (liquid) time to drain from the cheese into the bowl. Discard the whey. The cheese will be quite dry.
The 00 Tipo pizza flour used in this recipe is Italian flour suitable for pizza and pasta. (Do not substitute the 00 Tipo pastry flour!) The number of zeros refers to how finely ground the flour is, with one zero meaning the flour is less finely ground than double-zero flour.
