Dissolve the instant coffee in hot water and set aside to cool slightly.

In a mixing bowl, cream together the softened unsalted butter and icing sugar until light and fluffy.

Add the large beaten egg and mix well until fully incorporated.

In a separate bowl, whisk together the all-purpose flour, cornstarch, and ground cinnamon.

Fold the cooled coffee mixture into the creamed butter mixture and then gradually add the dry ingredients.

Transfer the dough into a piping bag and pipe onto a lined baking tray.

Chill the piped cookies in the freezer for about 5 to 10 minutes.

Preheat the oven to 350°F (175°C) and bake the cookies for approximately 8 minutes.

Allow the baked cookies to cool completely, then dip in melted chocolate and sprinkle with chopped pistachios.