2 cups whole milk
1 cup heavy cream
4 egg yolks
¼ cup lemon juice
2 teaspoons grated lemon zest
graham cracker crust crumbles (optional)
In a heavy-bottom saucepan, combine the milk and cream. Place over a medium-low heat and cook, stirring occasionally so a skin doesn’t form, until tiny bubbles start to form. Around the edges and the mixture reaches a temperature of 170 degrees.
Meanwhile, in a medium heat-proof bowl, whisk the egg yolks until smooth. Gradually whisk in the sugar until it is well incorporated and the mixture is thick and pale yellow. Temper the egg yolks by very slowly pouring in the hot milk mixture while whisking continuously. Return the custard to the saucepan and place over low heat. Cook, stirring frequently, until the custard is thick enough to coat the back of the spoon and it reaches a temperature of 185 degrees. Do not bring to a boil. (The recipe specifies to cook over low heat, but I felt the custard was taking a very long time to come to temperature that way, so I turned up the heat a bit.)
Pour the custard through a fine-mesh strainer into a clean bowl and cool completely, stirring often. To cool the custard quickly, make an ice bath by filling a large bowl with ice and water and placing the bowl with the custard in it; stir until cooled. Once completely cooled, cover and refrigerate until very cold, at least four hours or overnight.
Remove the custard from the refrigerator and gently whisk in the lemon juice and zest. Pour the mixture into the container of an ice cream machine and churn according to the manufacturer’s instructions. Add the graham cracker crust crumbles five minutes before the churning is completed, if using. Transfer to an airtight container and freeze for at least two hours before serving.