In a bowl, whisk together egg yolks and 1/4 cup of the sugar. Heat milk, cream, salt and remaining 1/4 cup sugar in a medium pot until simmering. Remove from heat and slowly whisk into egg-sugar mixture to temper. Pour back into pot and set over medium heat. Stir constantly until mixture coats the back of a wooden spoon (170° to 180°), about 4 to 8 minutes. Pour through a strainer into a new bowl. Stir in peanut butter until melted. Cool over an ice bath or in refrigerator.
Process in an ice cream maker according to manufacturer's directions. Transfer to a lidded, preferably flat, container. In a small bowl, stir jelly well, until very loose. Using the back of a spoon or a long toothpick, swirl jelly into ice cream. Freeze at least 2 hours.