Let's cook.
In a small bowl, combine the saffron threads with 1 tablespoon of hot water and let it steep for 5 minutes to release its color and aroma.
In a medium saucepan, whisk together the whole milk, granulated sugar, and cornstarch until the cornstarch is fully dissolved and there are no lumps.
Place the saucepan over medium heat and cook, stirring constantly with a whisk, until the mixture begins to thicken, about 8-10 minutes. Do not let it boil vigorously.
Once thickened to a pudding consistency, remove the saucepan from the heat. Stir in the steeped saffron mixture and the rosewater.
Pour the pudding into individual serving bowls or ramekins. Allow it to cool at room temperature for about 15 minutes.
Cover the bowls with plastic wrap and refrigerate for at least 2 hours, or until thoroughly chilled and set.
Before serving, garnish each pudding with a sprinkle of chopped pistachios.
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