01 - In a medium saucepan, combine the heavy cream, whole milk, granulated sugar, and salt. Heat over medium, stirring continuously until the sugar fully dissolves and the mixture begins to steam. Do not allow it to boil.
02 - In a medium bowl, whisk the egg yolks thoroughly. Slowly drizzle about ½ cup of the hot cream mixture into the yolks while whisking constantly to temper them. Gradually whisk the warmed yolk mixture back into the saucepan.
03 - Cook the custard over low heat, stirring constantly, until it thickens enough to coat the back of a spoon, approximately 5 to 7 minutes. Do not let the mixture boil.
04 - Remove the saucepan from heat. Stir in the raspberry extract, lemon extract, vanilla extract, and blue food coloring until fully blended and the desired shade of blue is achieved.
05 - Pour the custard through a fine mesh sieve into a clean bowl. Allow it to cool to room temperature, then cover and refrigerate for at least 4 hours or overnight for best results.
06 - Churn the chilled base in an ice cream maker following the manufacturer's instructions until it reaches a thick, creamy consistency.
07 - Transfer the churned ice cream to a lidded freezer-safe container. Freeze for at least 2 hours before serving to achieve a firmer texture.