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1
Plan ahead: Make sure the bowl of your ice cream machine is in the freezer for at least 24 hours before you churn.
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2
Combine the cream, milk, sugar, and salt in a saucepan and set over medium-low heat. Meanwhile, cut the kernels off the cobs of corn, then break each naked cob in half. Add the kernels and cobs to the cream mixture. Bring to a boil, then turn off the heat, cover, and let steep for an hour.
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3
Remove and discard the cobs. Add the mixture to a blender. Remove the keyhole from the lid. After you close the lid of the blender, top firmly with a kitchen towel that you don't mind getting dirty. Blend on high speed until the mixture is as smooth as possible.
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4
Return this to the saucepan, again over medium-low heat. Add the yolks to a heatproof bowl and whisk a bit. Add a splash of the hot corn mixture and whisk. Add another splash and whisk. Repeat this until you've added about 2/3 of the liquid. Now pour this back in the saucepan. Continue cooking-stirring slowly but constantly-until it thickens enough to coat the back of a spoon.
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5
Pour through a fine-mesh sieve into a heatproof bowl. Stir in the buttermilk and vanilla. Chill completely in the fridge.
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6
Just before churning, add the cider vinegar and adjust that, the vanilla, and salt to taste. Churn in an ice cream machine according to the manufacturer's instructions, then freeze for a few hours before serving.
