Season Paste: If your pistachio paste is from raw pistachios, taste it and add a pinch of salt to bring out the pistachio flavor if needed.
Prep Pot: Combine the majority of the milk (reserving 1/4 cup), pistachio paste, egg yolks, vanilla extract, and sugar in a saucepan. Whisk until well blended.
Cook: Heat the mixture on medium until it almost boils, stirring regularly to prevent the egg from cooking.
Prepare Starch Slurry: In a separate bowl, mix the reserved milk with cornstarch to form a smooth slurry.
Add Starch Slurry: Once bubbles appear in the saucepan, remove from heat and quickly stir in the starch slurry.
Thicken: Return the saucepan to the stove, cook on low to medium heat while stirring until the mixture thickens and bubbles (about 2-4 minutes).
Finish Cooking: Remove from heat and whisk for another minute to ensure a smooth consistency.
Add White Chocolate: Add chopped white chocolate, wait 30 seconds, then stir until melted and mixed in.
Taste Test: Adjust the flavor with additional sugar or vanilla if needed.
Strain (Optional): Strain through a sieve to remove any lumps or cooked egg bits.
Chill: Cover with plastic wrap touching the cream's surface, cool at room temperature for 30 minutes, then refrigerate until chilled.
Whisk and Use: Before using, break up the chilled cream with a fork, then whisk until smooth and ready for piping.