Heat the heavy cream and half-and-half in a 2 1/2-qt saucepan over medium-high heat. When hot, add 1/2 cup sugar. Stir to dissolve and bring the mixture to a boil, about 10 to 12 minutes. While the cream is heating, place the egg yolks and the remaining 1/4 cup sugar in the bowl of an electric mixer fitted with a paddle. Beat the yolks on high for 2 to 2 1/2 minutes, then scrape down the sides of the bowl. Beat on high, until slightly thickened and lemon-colored, and additional 2 1/2 to 3 minutes. (At this point, the cream should be boiling. If not, adjust mixer speed to low and continue to mix until the cream boils. If this is not done, the egg yolks will develop undesirable lumps.) Pour the boiling cream into the beaten egg yolks and whisk to combine. Return to the saucepan and heat over medium-high heat, stirring constantly, until the cream reaches a temperature of 185 degrees, 2 to 4 minutes. Add the rum and combine thoroughly. Remove from the heat and transfer to a stainless steel bowl. Cool the mixture in an ice-water bath to a temperature of 40 to 45 degrees, about 20 minutes. When the mixture is cold, freeze in an ice-cream freezer following the manufacturers instructions. Transfer the semifrozen ice cream to the plastic container that is holding the chocolate pecan crunch. Stir with a rubber spatula to thoroughly combine the crunch with the semifrozen ic cream. Securely cover the container, then place in the freezer several hours before serving. Serve within 3 days. Source: Death By Chocolate Cookbook by Marcel Desaulniers