01 - In a medium saucepan, combine the heavy cream, whole milk, granulated sugar, and salt. Set over medium heat, stirring gently until the sugar fully dissolves and the mixture begins to steam. Do not allow it to reach a boil.
02 - Place the egg yolks in a medium bowl and whisk lightly. While whisking constantly, slowly drizzle in about ½ cup of the hot cream mixture to gradually raise the temperature of the yolks without scrambling them.
03 - Pour the tempered yolk mixture back into the saucepan, stirring to combine. Cook over low heat, stirring constantly, for 5 to 7 minutes until the custard thickens enough to coat the back of a spoon. Keep the heat low and never let it boil.
04 - Remove the saucepan from heat. Stir in the raspberry extract, lemon extract, vanilla extract, and blue food coloring. Mix until the color is uniform and vibrant, adjusting the food coloring drop by drop until the desired shade is reached.
05 - Pour the custard through a fine mesh sieve into a clean bowl to remove any cooked egg bits. Let it cool to room temperature, then cover tightly and refrigerate for at least 4 hours or overnight for the best results.
06 - Pour the thoroughly chilled custard into an ice cream maker and churn following the manufacturer's instructions until the mixture is thick, creamy, and has soft-serve consistency.
07 - Transfer the churned ice cream into a lidded freezer-safe container. Smooth the surface, press a piece of parchment against the top to prevent ice crystals, and freeze for at least 2 hours before scooping and serving.