This makes about 2 quarts of ice cream.
In a food processor or blender, blend your grapes until the mixture is purple and liquid-y. Pour through a mesh siv to remove the seeds and skins, pressing to get as much liquid out as possible.
Transfer the liquid into a small saucepan, and stir in the sugar and cornstarch. Cook over medium heat, stirring frequently, until the mixture is thickened. Remove from heat and pour into a bowl to chill in the fridge for 30 minutes to an hour.
In a medium bowl, whisk together the milk, 1/2 cup heavy cream, and instant vanilla pudding mix. Set aside to thicken. In a large bowl, beat the remaining 2 cups of cream until soft peaks form. Then add in the powdered sugar, vanilla extract, and salt, and beat until stiff peaks form.
Fold the vanilla pudding mixture into the whipped cream until completely combined. That's your base! In either two loaf pans or two quart-sized containers, start by spooning a layer into the bottom of the vanilla base. Then, spoon some of your grape curd on top, and use a knife to swirl it in. Then, layer more vanilla cream, and repeat the process until your containers are full and all the mixtures have been used.
Freeze for at least 6 hours. When serving, leave on the counter for 5 minutes to help make scooping easier. Enjoy!