Nutrition per serving may change if servings are adjusted.
4 cups nonfat milk, divided
¼ cup corn syrup
3 large egg yolks
¼ cup cornstarch
2 tablespoons vanilla extract
2½ cups Marshmallow Fluff
Combine 3¾ cups milk and corn syrup in a large heavy saucepan. Heat over medium heat, stirring to dissolve the corn syrup, until steaming. Meanwhile, whisk together egg yolks, cornstarch and the remaining ¼ cup cold milk in a medium bowl until smooth. Gradually whisk 1 cup hot milk into the egg-yolk mixture; then pour the egg-yolk mixture into the hot milk in the pan. Cook over medium heat, whisking constantly until the mixture boils and thickens, 3 to 5 minutes. (Because the custard is thickened with cornstarch, it will not curdle when it boils.)
Transfer the custard to a large clean bowl and place a piece of wax paper directly over the surface to prevent a skin from forming. Cool completely. Whisk in Fluff and vanilla until as smooth as possible. (The mixture will be a little lumpy; lumps will break down during stir-freezing.) Pour into the canister of an ice cream maker and freeze following the manufacturer's instructions.