Step 1: Prepare the Crust

1. Preheat your oven to 325°F (160°C) and line a muffin tin with paper liners.
2. In a medium mixing bowl, combine the crushed digestive biscuits, finely chopped pistachios, and melted butter. Mix until the texture resembles wet sand.
3. Spoon about 1 tablespoon of the crust mixture into each muffin cup. Use the back of a spoon or a flat-bottomed glass to press the crust firmly into the bottom of each liner.
4. Bake the crusts for 5 minutes, then set aside to cool slightly while you prepare the filling.

Step 2: Make the Cheesecake Filling

1. In a large mixing bowl, beat the softened cream cheese and sugar together until smooth and creamy, about 2-3 minutes.
2. Add the sour cream, egg, and vanilla extract, and mix until just combined.
3. Stir in the dissolved instant coffee and flour, blending until the mixture is uniform in color and smooth.
4. Spoon the cheesecake filling evenly over the crusts in the prepared muffin cups, filling each about ¾ full.

Step 3: Bake and Cool

1. Bake the mini cheesecakes at 325°F (160°C) for 18-20 minutes, or until the centers are just set. They may appear slightly jiggly, which is perfect as they will firm up while cooling.
2. Turn off the oven, crack the door slightly, and allow the cheesecakes to cool for 10 minutes in the oven to prevent cracking.
3. Remove from the oven and let the cheesecakes cool completely on a wire rack.
4. Once cooled, refrigerate for at least 2 hours, or until thoroughly chilled and set.

Step 4: Garnish and Serve

1. Just before serving, top each cheesecake with a sprinkling of chopped pistachios.
2. For a touch of indulgence, add a dollop of whipped cream and a drizzle of coffee syrup or chocolate ganache.
3. Serve immediately or keep refrigerated until ready to enjoy.