How to Make It
Line a strainer with a double layer of cheesecloth and set over a large bowl. In a large saucepan, heat the milk and cream over moderately high heat to 180°. Remove from the heat and slowly add the vinegar until you see the milk separate; add more vinegar as needed. Cover the saucepan and let stand for 2 minutes.
Pour the contents of the saucepan into the strainer and shake vigorously to remove the water (a.k.a., whey). You should have about 2 cups of ricotta; let cool.
Preheat the oven to 325°. Butter four 1-cup ramekins. In a large bowl, whisk 1 3/4 cups of the ricotta with the heavy cream and lemon zest, breaking up any large ricotta curds; season with salt and pepper. Whisk in the eggs.
Pour the pudding into the prepared ramekins and set them in a baking dish. Add enough hot water to the dish to reach halfway up the sides of the ramekins. Bake for about 55 minutes, or just until set. Let the puddings cool to room temperature or refrigerate until chilled. Serve the puddings in the ramekins.