In a food processor, pulse the toasted shelled pistachios, all-purpose flour, and salt until you achieve a sandy texture—about 30 seconds. Next, pour in the melted unsalted butter and pulse again until the mixture is combined and crumbly, which should take another 15 seconds.

Press approximately 1 tablespoon of the crust mixture firmly yet gently into the bottom of each muffin cup of a lined or greased muffin pan. Preheat your oven to 325°F (163°C) while you continue to the next step.

In a mixing bowl, beat the cream cheese and powdered sugar together using an electric mixer on medium speed for about 2 minutes until the mixture is smooth and creamy. Slowly add in the large egg, vanilla extract, and pistachio flour, mixing until just combined.

Spoon the rich filling evenly over the crust in each muffin cup, ensuring they are filled just to the top. Bake in the preheated oven for 18 minutes, or until the edges are set while the centers still have a slight jiggle.

Remove the muffin pan from the oven and allow the cheesecakes to cool in the pan for 1 hour. After cooling, transfer them to the refrigerator and chill for at least 2 hours before serving.