Preheat the oven to 325 degrees. Spray the springform pan with cooking spray. Separate the eggs, placing the whites in one of the large bowls and the yolks in the work bowl of a food processor.
Add the sugar and vanilla to the work bowl of the food processor and process until thick and light yellow, about 1 minute. Add the ricotta and zest and process until smooth, another 30 seconds. Scrape the mixture into the other large bowl.
Beat the whites on high speed with the mixer until they hold stiff peaks. Fold the whites into the ricotta mixture and scrape into the prepared pan, smoothing the top with the spatula.
Bake until the cake is deep golden brown and the sides begin to pull away from the pan, about 1 hour and 20 minutes. Transfer to the rack to let cool completely. Cover with plastic wrap and refrigerate until serving, at least 6 hours and up to 1 day. To serve, release the sides of the springform pan, dust with confectioners' sugar using the strainer, and cut into wedges.
Recipe courtesy of Instant Gratification, Lauren Chattman, William Morrow/HarperCollins