01 - Combine heavy cream, whole milk, and granulated sugar in a medium saucepan. Heat over medium, stirring occasionally, until the mixture just begins to steam and the sugar has fully dissolved. Do not allow it to boil.
02 - In a separate mixing bowl, whisk the egg yolks thoroughly. Slowly drizzle about 1/2 cup of the hot cream mixture into the yolks while whisking constantly to gradually bring the temperature up without scrambling the eggs.
03 - Pour the tempered egg yolk mixture back into the saucepan. Cook over low heat, stirring constantly with a wooden spoon or spatula, until the custard thickens slightly and coats the back of the spoon, reaching 170–175°F. This should take about 5 to 7 minutes.
04 - Pour the custard through a fine-mesh sieve into a clean bowl to remove any cooked egg bits. Allow it to cool for 10 minutes at room temperature.
05 - Stir in the lemon juice, almond extract, raspberry extract, vanilla extract, and blue raspberry drink mix powder if using. Add blue food coloring drop by drop until the desired vibrant blue shade is achieved.
06 - Cover the bowl and refrigerate for at least 4 hours, or preferably overnight, until the mixture is thoroughly chilled.
07 - Pour the chilled mixture into your ice cream maker and churn according to the manufacturer's instructions until it reaches a soft-serve consistency.
08 - Transfer the churned ice cream to a freezer-safe container, cover tightly, and freeze for at least 2 hours to firm up before scooping and serving.