1. Heat the cream in a medium saucepan over medium until hot. While the cream heats, whisk together the egg yolks, sugar and salt in a bowl. Gradually add the hot cream to the yolk mixture, whisking constantly. Return the mixture to the saucepan over medium-low heat and cook, stirring constantly with a wooden spoon until the mixture is thick enough to coat the back of a spoon, 7-8 minutes. Remove from the heat and stir in the milk and vanilla extract. Add 2 cups of the marshmallow fluff and stir until smooth. Pour the mixture into a clean bowl set in a larger bowl filled with ice water. Cool completely stirring often. Transfer to the refrigerator and chill completely.
2. Stir together the remaining 1/4 cup marshmallow fluff and the chocolate syrup until smooth.
3. Pour the chilled custard into an ice cream maker and freeze according to manufacturers directions. Transfer 1/2 of the ice cream into an 8-inch square baking dish. Swirl in 1/2 of the chocolate mixture and sprinkle with 1/2 of the nuts. Top with the remaining ice cream and repeat with remaining chocolate mixture and nuts. Freeze at least 3 hours before serving.
