12 eggs, separated
3 cups white sugar, divided
16 fluid ounces dark rum (such as Captain Morgan® Spiced Rum)
1 teaspoon ground nutmeg
2 cups heavy whipping cream
1 quart half-and-half
Mix egg yolks, 2 cups sugar, rum, and nutmeg together in a large bowl. Cover with plastic wrap and refrigerate 8 hours to overnight to "cure."
Beat egg whites and remaining 1 cup sugar in a bowl using an electric mixer until firm peaks form. Fold in heavy cream. Fold in the egg yolk mixture. Beat in half-and-half until well combined. Pour into lidded jars or containers, refrigerate, and shake before serving.