Preheat the oven to 350 degrees F. Grease a 13-by-9-by-2-inch baking pan with butter.
Using a double boiler over medium heat, cook the rice in the milk uncovered for 25 minutes, and then covered for another 25 minutes, until the rice is thoroughly cooked. If the rice is still a little too firm, let sit on the burner over low heat for another 10 minutes. Cool to room temperature.
While the rice is cooking, make your egg mixture by combining the egg yolks, vanilla and salt in a bowl. In another bowl, combine the sugar, cornstarch, lemon zest, cinnamon and nutmeg.
Add the egg yolk mixture, dry ingredient mixture, 3 tablespoons butter and the heavy cream to the cooled rice, mixing between each addition.
Pour the mixture into the prepared baking pan. Add the raisins, if using. Set the entire pan in a water bath and bake for 1 hour. If you use raisins, halfway through the baking you have to stir the bottom by sliding a knife along the sides (this is so the raisins will not gather at the bottom) without disturbing the custard. Bake until the rice pudding is no longer liquid. It will have solidified and a slight caramel colored crust will have formed on top. Cool and refrigerate until serving.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.