Step 1

Combine the blueberries and 1/4 cup sugar in a small pot. Place over medium heat and bring to a simmer. Let cook, stirring occasionally, until most of the fruit breaks down, about 12 to 15 minutes. Set aside to cool slightly.

Step 2

Combine the remaining 3/4 cup sugar, heavy cream, and salt in a medium pot. Place over medium heat and stir frequently, just until the sugar is dissolved (do not boil). Remove from heat.

Step 3

Meanwhile, whisk the egg yolks in a medium bowl. Remove 1/3 cup of the warm cream mixture from the pot. While whisking the yolks constantly, slowly drizzle the reserved 1/3 cup warm cream mixture into the egg yolks to bring them up to temperature. Transfer the warmed egg mixture to the pot with heavy cream, whisking well to combine.

Step 4

Return the pot to medium heat, stirring frequently with a rubber spatula to scrape the bottom and corners of the pan, until the mixture thickens enough to coat the back of the spoon (on a thermometer, the temperature should be between 160 and 180°). Immediately pour through a fine mesh strainer into a large bowl and set it over a bowl of ice water. Stir to cool the mixture slightly. Add the blueberry puree, vanilla, and buttermilk, then stir until the mixture is at room temperature. Cover and refrigerate the ice cream base for 4 hours until cold or overnight.

Step 5

Transfer to an ice cream maker and freeze according to the manufacturer's instructions. You can eat this directly from the machine, like soft serve, or transfer to a container to freeze for at least 4 hours, up to 48 hours, for the best texture and "scoopability."