Place the chopped white chocolate in a medium bowl.
Pour the heavy cream over the chocolate.
Microwave on high for 30-second intervals, or until chocolate is melted, and the mixture is whisked smooth. Do not overheat or you'll scorch the chocolate and/or cream.
Whisk in the eggnog, sugar, and rum.
Whisk in the egg yolks.
Place 4 greased ramekins or custard cups in an 8x8-inch baking pan.
Pour enough water into the baking pan that it rises to about halfway up the ramekins.
Pour the mixture evenly into the ramekins.
Bake at 325 degrees for 30-35 minutes, or until the custard is set at the edges, and slightly jiggly in the center.
Allow ramekins to cool for 20 minutes in the baking pan before removing to cool completely.
Refrigerate for at least 1-2 hours, or until chilled.
Top with whipped cream, and a sprinkle of nutmeg.