Add pistachios to your food processor fitted with the blade attachment. Processor until a smooth butter forms. This could take a little bit so have patience.

In a large mixing bowl, combine the sweetened condensed milk, pistachio butter and vanilla. Stir until thoroughly combined.

Pour the heavy whipping cream into a separate mixing bowl (see notes). Using a handheld mixer, mix on high-speed until stiff peaks form.

Add the whipped cream to the bowl with the pistachio mixture. Using a large spatula, gently and carefully fold the two together using big sweeps until combined and no streaks remain. Don't rush this step.

If using food coloring, add it now and fold it into the mixture.

Pour the ice cream base into a freezer-safe dish and sprinkle 1/2 cup of chopped pistachios over top. Alternatively, fold the nuts into the mixture before pouring into the pan.

Place the pan into your freezer for 4 hours or overnight.

Before serving, place the ice cream on the counter for 20 minutes or until soft enough to scoop. I also like to dip my ice cream scoop in hot water (shake off excess water) before scooping.