To prepare the Popcorn Ice Cream, heat 1 T butter in a big stock pot. Add corn and put the lid on, paying attention to turn it off after it all pops.
Heat 2 cups whole milk in a pan to a bare simmer, add 2 cups popcorn, cover and turn it off. Leave it until it’s room temperature, about 1 hour. Pour the mixture through a fine mesh strainer.
Return popcorn milk to pan, add 1 T butter and heat to medium.
In a separate bowl, combine 3 egg yolks and 1/3 cup sugar; whisk until smooth. Add a cup of warmed popcorn milk to the egg mixture and whisk vigorously.
Pour the warmed egg mixture back into the pan with remaining popcorn milk. Heat to 165 degrees, whisking constantly. Strain it again, then refrigerate completely.
Freeze according to ice cream maker directions. Serve with a little fleur de sel (sea salt).