In a small pot over medium-high heat, combine the corn and butter. Cook 10 minutes, until no longer frozen and most of the moisture has evaporated. Add the milk, heavy cream, and salt. Bring to a boil, then immediately remove from the heat and let sit 10-15 minutes to infuse. Transfer to a blender and puree until smooth. Pass through a fine mesh sieve into a bowl.

Preheat oven to 325 degrees F. Bring a kettle of water to a boil. Place 8 ramekins on a high rimmed baking sheet, with walls high as tall as the ramekins.

In a medium bowl, mix together the eggs, yolks, and sugar. Whisking constantly, stream in the strained, warm, pureed corn a little at a time to temper the eggs. Pour custard into a spouted vessel (to make pouring easier), or use a ladle to portion into the ramekins.

Pour the custard evenly into the 8 ramekins. Transfer to the center rack of the oven, then carefully pour in the water. Bake 30-40 minutes. The very center should have a wiggle to it when moved and will continue to cook out of the oven. Remove the ramekins from the water, transfer to a baking sheet, and cover with plastic wrap. Let the custard cool completely before serving, at least 6 hours, but preferably, allow the ramekins to refrigerate overnight.