In a small bowl, dissolve cornstarch in ½ cup of whole milk, stirring until smooth.

Heat remaining whole milk and sugar in a medium saucepan over medium heat until boiling.

Gradually whisk in cornstarch mixture, stirring continuously until thickened, about 5-7 minutes.

Remove from heat and cool quickly in an ice bath, stirring until room temperature.

Blend chopped beets with rose water until smooth and strain through a fine sieve.

Stir in beet-rosewater mixture, pinch of salt, heavy cream, and optional vanilla extract.

Refrigerate the mixture in an airtight container for several hours or overnight.

Churn in an ice cream maker according to the manufacturer's instructions, adding chopped pistachios during the last few minutes.

Transfer to an airtight container, smooth the top, cover with parchment paper, and freeze for at least two hours.