01 - In a medium saucepan, combine the whole milk, heavy cream, granulated sugar, and salt. Place over medium heat, stirring frequently, until the mixture is steaming but not boiling.
02 - In a separate mixing bowl, whisk the egg yolks until smooth. Gradually pour 1/2 cup of the hot milk mixture into the yolks while whisking constantly to gently temper them.
03 - Slowly pour the tempered yolk mixture back into the saucepan, whisking constantly. Continue cooking over medium-low heat, stirring continuously, until the custard thickens and coats the back of a spoon, approximately 5 to 7 minutes.
04 - Remove the saucepan from heat. Stir in the vanilla extract, raspberry extract, lemon extract, and almond extract until well combined. Add blue food coloring and mix until the color is evenly distributed throughout the custard.
05 - Pour the custard through a fine-mesh sieve into a clean bowl to strain out any cooked bits. Allow the mixture to cool to room temperature, then cover tightly and refrigerate for at least 3 hours until thoroughly chilled.
06 - Process the chilled custard in an ice cream maker following the manufacturer's instructions. Transfer the churned ice cream to a freezer-safe container, cover, and freeze for 1 to 2 hours or until firm.